If he wins this United States Open, Spieth, 21, will be the first man since Tiger Woods in 2002 to complete the first two legs of the Grand Slam. Woods was groomed from a young age to be a champion golfer. You have to look harder to see destiny’s fingerprints on Spieth.

For Greller, the only person whose opinion matters is Spieth, who has gotten better at communicating his needs. At the World Golf Championships event outside Miami in March, Spieth shot three rounds in the 70s and tied for 17th.

“It worked out great,” Shawn said. “It allowed Jordan to be a really mature 19-year-old when he turned pro.”

On the Sunday of the Masters, Harrison said, his wife, Suzanne, watched Spieth’s post-victory interviews and told him, “He’s so grounded and so humble, if his mom or dad ever chose to write a book on how to raise a Jordan Spieth, not the player but the person, it would be a best seller.”

“In team sports he’d get so upset if somebody else did something wrong,” Chris said, adding, “I’d have to remind him that nobody’s perfect.”

Spieth and his parents needed no persuading. When Spieth dropped out of Texas six months later, his father offered Greller the job. Jennifer Wong stood outside Greller’s classroom at Narrows View Intermediate School the day he broke the news to his 28 students that he was leaving.

Of course, overindulgence is always a risk, and wearing shoes that match one’s outfit but lack practicality means some attendees struggle toward the exit at the end of the day — but at the very least they look good doing it.

Spieth won his next tournament, captured the Masters a month later and has broken 70 in nine of his past 12 rounds.

Since the Masters, Spieth’s world has gotten at once bigger and smaller. His friends understand why he is sometimes reluctant to leave home.

With a master’s degree in business, Shawn ran, then sold, a mobile app company. His latest venture is MVPIndex, which uses statistical analysis and social media conversations in pro sports to help companies maximize the return on their sponsorship investments and athletes, teams and leagues to maximize their marketing reach.

Shawn dreamed of playing in the N.B.A., but he recognized he had a better chance of flying to the moon. Being a grounded sort, he threw his energy into baseball. He pitched American Legion games, sometimes against Jamie Moyer, who went on to a 25-year career in the majors, and he played baseball at Lehigh.

Sports in Their Blood

“It seems that all Jordan does is find a pool table when he is on the road because he seems to become better each time he returns home,” Simmons said.

“Especially with the boys, because they were so close in age, we always wanted to make sure we supported them equally,” Chris said. “So we would divide and conquer.”

“Annie’s good for Jordan,” Spieth’s mother said. “He doesn’t need a celebrity girlfriend. He doesn’t want the attention.”

“Mike’s my right-hand man,” Spieth said, adding, “He’s the only one I can trust out there on the course.”

On the road, Spieth tries to rent homes near the tournament site whenever possible (and, yes, many of the properties have pool tables).

Visitors to Royal Ascot have tickets to one of three different areas: the Royal Enclosure, the Grandstand or the Silver Ring. Each section has its own dress code. The Royal Enclosure, which is by invitation only, has the strictest rules, while the Silver Ring is as close to casual as anyone attending can get, but it is still by no means a place to wear your favorite sports jersey.

“They came out with tears streaming down their faces, they were so sad to be losing this great teacher,” said Wong, now the school principal.

In 2013, when Spieth was playing in Woods’s event in Southern California, he was approached by Bruce Jenner, who struck up a conversation and offered to introduce Spieth to his daughter Kendall. Spieth walked away baffled. He had not kept up with the Kardashians and did not know who they were.

Spieth met Simmons on the first day of science class. At basketball games, Spieth became acquainted with Leyendecker, who served all four years as the team manager.

The Grandstand, where Reeve and her friends gather, is slightly more relaxed, but only slightly. Women still must wear a headpiece, and strapless dresses, exposed midriffs and shorts are forbidden. Men can leave their top hats at home, but they are required to wear suits and ties with the proper accompanying shoes. The news media must match this attire to be allowed to cover the races.

Spieth called Greller afterward and practiced his assertiveness by telling Greller to be more assertive. He told him not to hesitate to call him off shots in certain situations, especially on the weekends.

“The most important thing is probably my family and our team,” Spieth said, adding, “They’re all dedicated to the same goals that I have.”

That is by design, as the course requires its patrons to adhere to strict dress codes.

Spieth loved that one. Flattery will get you nowhere with Spieth, who values facetiousness. The common thread running through his hodgepodge of an entourage is the needle, liberally applied to prick Spieth’s ego. His inner circle includes a former sixth-grade teacher, his ninth-grade science lab partner, a onetime high school basketball team manager, a junior golf nemesis from Kentucky and his sister, who has special needs.

There are the parents who never put him on a pedestal, the swing coach whom he was introduced to at age 12 and has worked with since, the girlfriend he has dated since he was 17 and the best friends he has known longer, and the educator turned caddie.

“Lately it’s been an adjustment going out in public,” Leyendecker said. “Now that he’s won the Masters a lot more people recognize him as soon as he walks out, and he’s too nice of a guy to not acknowledge people. So Blaine, Hays and I have to sometimes be the villains and pry him away.”

“The most significant influence, without a doubt, in all our lives is Ellie,” Shawn said.

Chris played basketball at Moravian College, and once ranked among the top free-throw shooters in N.C.A.A. Division III. She was working as a computer engineer at Neiman Marcus when she gave birth to Jordan, who was named after his father’s favorite athlete, Michael Jordan.

Women must wear dresses or skirts that fall just above the knee as a minimum and will be pulled aside if their dresses are deemed too short. The shoulder straps of all tops must be one inch wide or greater, midriffs must be covered and hats are required. All headpieces must have a base of four inches or more. Trouser suits adhering to these principles are allowed. Jackets and pashminas are also permitted, but the shoulder-strap rules still apply even if they are covered by such garments.

At tournaments, the role of the villain is played by Spieth’s manager, Jay Danzi, and Danzi’s associate Jordan Lewites. “They’re already trained at saying no,” Spieth said.

Last month, Jordan was in the middle of a round at the Byron Nelson, his hometown tournament, when Ellie, who was standing against the gallery ropes with their mother, screamed his name. Jordan’s mask of concentration dropped at the sound of her voice, and he trotted over and gave her a hug before hitting his next shot.

Between shots in the first round, they wondered if maybe they ought to stop giving Spieth grief about not finishing college.

The Spieths have two other children, Steven, a rising junior on the basketball team at Brown, and Ellie, 14. The boys, who are 18 months apart, played soccer, basketball, baseball and football when they were young. Jordan was a promising left-handed pitcher, but he gave up baseball at 12.

His Right-Hand Man

“It’s not easy to caddie for Jordan,” Spieth’s mother said.

“We always bring it back up because we sometimes joke about what would happen on the PGA Tour in a similar situation where I just had to show up and start caddying on the fly if for some reason Michael got hurt,” he added.

Spieth’s coach, Cameron McCormick, attends only a few tournaments a year. Verret completed work on her business degree at Texas Tech in December and is employed full time as an event coordinator for the First Tee of Greater Dallas. She has a limited number of vacation days to spend with Spieth on the road.

His sister’s limitations, once tests of patience, have become a source of perspective. Jordan has said repeatedly that he is humbled daily by her struggles.

The Spieths hewed to the philosophy that if every sibling is important, no sibling is important.

Spieth has taken the modern celebrity script and turned it upside down. Rather than projecting himself onto the world’s smartphones, tablets and televisions to increase his star power, he is pursuing normalcy through a conspicuously low-wattage life.

He dropped the bag at his son’s feet and started to walk away. He did not get far. Spieth apologized, and father and son finished the week as a team.

The Byron Nelson tournament was one of the rare weeks in which his gang was all there. Simmons and Leyendecker, both of whom graduated from college this year, stayed at Spieth’s house early in the week and graced his large galleries once the tournament started.

UNIVERSITY PLACE, Wash. — Well before Jordan Spieth was fitted for a Masters green jacket in April, he acquired a nickname from a few PGA Tour players, who took one look at his pinchable face, impeccable manners and bulletproof game and anointed him the Golden Child.

Spieth would agree. In his second PGA Tour start as a pro, at Pebble Beach in 2013, he came off the course after a round of 70 that he thought should have been better and said, “I couldn’t have caddied for myself today.”

In his early teenage years, Jordan occasionally traveled to out-of-town tournaments on his own because his parents were occupied with his siblings. He shared a hotel room with another player or stayed with a host family, which hastened his self-sufficiency.

Entourages on the tour have grown to resemble pit crews, with players relying on swing coaches, mental coaches, conditioning coaches, chiropractors, spiritual guides, statistical wizards, managers, publicists and even yoga instructors to fine-tune their game and their brand.

Mark Harrison, the executive director of the Northern Texas P.G.A., was also at the Byron Nelson to see Jordan. Through his charitable foundation, Spieth has become involved in Harrison’s efforts to attract more youngsters to golf.

“I enjoy working at something that is impossible to conquer,” Jordan said.

She and her friends, some of whom have been attending Ladies’ Day for 16 years, pool their money and bet as a group. The day started well as they won £67 (about $106) when Waterloo Bridge finished first in the first race, so smiles were not hard to find. By the end of the day, the champagne bottles were empty, and they had picked enough winners to break even.

Spieth was trying to become the first player since Woods to win multiple Junior Amateur titles. On the opening hole of their first practice round, Greller said, he was so nervous he gave Spieth the wrong yardages. They were playing the 10th, but Greller gave Spieth numbers for the first. Greller settled in, and Spieth won the title.

“When I was a teacher, I tried to create a climate where if the student did make a mistake, you created some learning moment from it,” Greller said. “It’s the same out here. We’re going to make mistakes every day. Jordan is such a cerebral person, he’s able to learn from them much quicker than just about any other person.”

The occasion also doubles as a great excuse to get together with friends. This year, Reeve and her group secured a prime spot at a wooden table on the outdoor Brigadier Gerard Lawn — many locations at Ascot are named for famous racehorses — where they could see the procession led by Queen Elizabeth II as well as all the runners making their way to and from the track.

He has grown to realize, at least intellectually, that he cannot hit every shot perfectly. He has matured a lot since his father caddied for him at the Texas State Amateur one year and threatened to quit midway through the round because he had grown tired of listening to Spieth’s griping about bad breaks and worse shots.

The rules are held sacred by many, and the older generations often keep watch on the younger ones. Or as one woman told her companion near the parade ring: “The young ones try to get away with shorter hemlines every year.”

Greller’s background made him perhaps uniquely qualified to work with Spieth. It turns out that sixth graders in the classroom are not so different from Spieth on the course. Their emotions are up and down, and they are gaining an awareness of their limitations and their potential.

Jordan acquired a plastic driver and toy putter when he was a toddler. He loved to hit with them so much his mother used them as incentives for potty training.

She added: “He was such a constant and steady presence. He has a knack for meeting kids right where they are and knowing what they need. It’s a rare quality.”

An Entourage Takes Shape

The school’s motto is “Men for Others,” and the name tags, a must for freshmen, are intended to drive home the point that in an environment where everyone is a servant, no one is special.

Document | Royal Ascot Style Guide The five-day Royal Ascot meet in England requires its patrons to adhere to strict dress codes.

But there is a lot more to Greller’s job than carrying Spieth’s bag and cashing checks.

Whenever Spieth comes off the road, he invites his friends over and they grill out and uncork a bottle of wine. His dining table flips to become a poker table. They also entertain themselves with billiards and games of H-O-R-S-E on the mini basketball hoop in the living room.

Spieth is not afraid to poke fun at himself in public, as he did in his victory speech at the Masters when he referred to his hairline. His fearless, aggressive play on the course and his modest, muted style off it have turned him into golf’s flavor of the month — not vanilla, but not rocky road, either. More like cinnamon spice.

The next year, with Greller on his bag, Spieth finished as the low amateur at the United States Open. Before the Open, Greller attended the N.C.A.A. championship, where Spieth helped Texas to the title. He struck up a conversation with one of Spieth’s friends, Eric Leyendecker, who came away impressed. Leyendecker said he told Spieth he should consider hiring Greller when he turned pro.

As he did when he was a teacher, Greller has reached out to tour veterans for advice so he can improve his performance.

The boys also took piano lessons. “Jordan loved it, Steven hated it,” Chris said, adding: “Jordan loved it because his instructor would put him in local competitions. If she didn’t let him compete at it, he would not have worked at it as much.”

Basketball, not golf, is at the heart of Spieth’s story. His parents, Shawn and Chris, grew up in the same small town in Pennsylvania’s Lehigh Valley. They started out as friends and fellow basketball gym rats before becoming sweethearts at Saucon Valley High School.

“I didn’t have my best week caddying,” Greller said. “I told my wife, ‘Remind me of how bad I feel as a caddie right now so I can appreciate the highs.’ ”

Greller, who played golf for Northwestern College in Iowa before earning his master’s in teaching from George Fox University in Oregon, was teaching outside Seattle in 2006. A volunteer caddying stint at the United States Public Links, held near his Gig Harbor home, changed his life. Greller enjoyed the experience so much, he switched school districts so he could moonlight as a caddie at Chambers Bay.

Spieth had been written up in the local newspapers for his junior golf exploits by the time he enrolled as a ninth grader at Jesuit College Preparatory School, an all-boys school. Like all freshmen, though, he wore a name tag to complete his uniform of khaki pants, a dress shirt, tie, blazer, and black or brown shoes.

Once, several years ago, Chris said, Jordan looked at her during one of Ellie’s tearful fits and asked plaintively, “Can’t you put her in a timeout?”

Over all, the Ladies’ Day crowd is there to see and be seen as the horses parade by for six carded races, which include the 4,000-meter Group I Gold Cup, won by Trip To Paris this year.

The Silver Ring has no specific requirements on what you are required to wear but does restrict specific types of clothing, like sport replica shirts. Racegoers there are still highly encouraged to dress smartly. The various dress codes are no secret, and Ascot does monitor attendees to make sure they are adhering to the rules.

If the family revolved around any child, it was Ellie, who was born with a neurological disorder that left her developmentally disabled. Her life is a happy dance interrupted by cloudbursts of frustrating setbacks like drawing with a pen that dries up or misplacing one of the keychain souvenirs Jordan brings back from his travels.

After all, noted Leyendecker, “He got his Masters before we got our bachelor’s.”

For those who are more interested in fashion than horses, Thursday is the day to attend Royal Ascot, which traditionally runs from a Tuesday through a Saturday in mid-June each year. Thursday’s race card as a whole might not be as robust as the other days, but it is set aside as Ladies’ Day, meaning the women go all out to impress.

Its website explains: “Royal Ascot is synonymous with sartorial elegance. This is upheld by our dress code, which invites guests to contribute to an occasion heralded as a major fashion event in its own right.”

His other peer group, consisting of friends he grew up with in Dallas, gave him a different nickname. Taking note that he left the University of Texas midway through his sophomore year to try his luck as a professional golfer, his childhood clique took to calling him the College Dropout.

Spieth was the only serious golfer in the group, but he talked Leyendecker into trying out for the team as a senior, and Leyendecker took away from the experience one of his most cherished high school memories.