SEATTLE -- Spend time with the family of Bill Gates, and eventually someone will mention the water incident.

The future software mogul was a headstrong 12-year-old and was having a particularly nasty argument with his mother at the dinner table. Fed up, his father threw a glass of cold water in the boy's face.

"Thanks for the shower," the young Mr. Gates snapped.

The incident lives in Gates family lore not just for its drama but also because it was a rare time that Bill Gates Sr., father of his famous namesake, lost his cool. The argument presaged a turning point in the life of a tempestuous boy that would set him on course to become the Bill Gates whom the public knows as co-founder of Microsoft Corp. and the world's richest man.

Behind the Bill Gates success story is the other William Gates. The senior Mr. Gates balanced a family thrown off kilter by a boy who appeared to gain the intellect of an adult almost overnight. He served as a quiet counsel as his son jumped into and thrived in the cutthroat business world. When huge wealth put new pressure on the son, the elder Gates stepped in to start what is now the world's largest private philanthropy.

Gates Family Album

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Sean Flanigan for The Wall Street Journal

William H. Gates at his home in the Laurelhurst neighborhood of Seattle, WA.

Bill Gates Sr., 83 years old, is now co-chair of his son's $30 billion philanthropy, the Bill & Melinda Gates Foundation. He has avoided the spotlight. The public details of his life include little beyond his official biography at the foundation, which says he was a Seattle lawyer, World War II veteran, nonprofit volunteer and father of three. He has compiled his thoughts on life in a short book to be published next week.

In interviews with The Wall Street Journal, Bill Gates Sr., Bill Gates and their family shared many details of the family's story for the first time, including Bill Gates Jr.'s experience in counseling and how his early interest in computers came about partly as a result of a family crisis. The sometimes colliding forces of discipline and freedom within the clan shaped the entrepreneur's character.

The relationship between father and son entered a new phase when the software mogul began working full-time seven months ago at the Gates Foundation. For the past 13 years, the father has been the sole Gates family member with a daily presence at the foundation, starting it from the basement of his home and minding it while his son finished up his final decade running Microsoft. They now work directly together for the first time.

At six-foot-six, Bill Gates Sr. is nearly a full head taller than his son. He's known to be more social than the younger Bill Gates, but they share a sharp intellect and a bluntness that can come across to some as curt. He isn't prone to introspection and he plays down his role in his son's life.

"As a father, I never imagined that the argumentative, young boy who grew up in my house, eating my food and using my name would be my future employer," Mr. Gates Sr. told a group of nonprofit leaders in a 2005 speech. "But that's what happened."

The first stage -- argumentative young boy -- "started about the time he was 11," Mr. Gates Sr. says in one of a series of interviews. That's about when young Bill became an adult, says Bill Sr., and an increasing headache for the family.

Until that time, the Gates home had been peaceful. Bill Sr. and his wife, Mary, had three children: Kristi; then Bill, born in 1955; and Libby. It was a close family that thrived on competitions -- board games, cards, ping-pong. And on rituals: Sunday dinners at the same time every week, and at Christmas, matching pajamas for every family member.

While very involved in his kids' lives, Mr. Gates Sr. was somewhat distant emotionally, which his children say probably reflects his generation. His stature, combined with a lawyerly bent for carefully choosing his words, also made him intimidating at times. "He'd come home and he'd sit in a chair and eat dinner, but there was never any kind of warm, give-me-a-hug kind of thing," says Kristi Blake, his oldest daughter.

Mr. Gates Sr. left much of the day-to-day parenting to his wife while he was building his career at a Seattle law firm. Daughter of a Seattle banker, Ms. Gates had been an athlete and top student in high school and college, where she met Bill Sr. She became a full-time volunteer and served on corporate boards.

Ms. Gates encouraged her kids to study hard, play sports and take music lessons. (Bill Gates tried the trombone with little success.) And she imparted a discipline that reflected her upbringing in a well-to-do family. She expected her kids to dress neatly, be punctual and socialize with the many adults who visited their home. For the most part, young Bill dutifully abided.

"She was the most engaged parent and she had high expectations of all of us," says Libby Armintrout, Bill's younger sister. "Not just grades and that sort of thing, but how we behaved in public, how we would be socially."

A Battle of Wills

Bill Gates at an early age became a diligent learner. He read the World Book Encyclopedia series start to finish. His parents encouraged his appetite for reading by paying for any book he wanted.

Still, they worried that he seemed to prefer books to people. They tried to temper that streak by forcing him to be a greeter at their parties and a waiter at his father's professional functions.

Then, at age 11, Bill Sr. says, the son blossomed intellectually, peppering his parents with questions about international affairs, business and the nature of life.

"It was interesting and I thought it was great," Mr. Gates Sr. says. "Now, I will say to you, his mother did not appreciate it. It bothered her."

The son pushed against his mother's instinct to control him, sparking a battle of wills. All those things that she had expected of him -- a clean room, being at the dinner table on time, not biting his pencils -- suddenly turned into a big source of friction. The two fell into explosive arguments.

"He was nasty," Ms. Armintrout says of her brother.

Mr. Gates Sr. played the role of peacemaker. "He'd sort of break them apart and calm things down," says Ms. Blake, the eldest sibling.

The battles reached a climax at dinner one night when Bill Gates was around 12. Over the table, he shouted at his mother, in what today he describes as "utter, total sarcastic, smart-ass kid rudeness."

That's when Mr. Gates Sr., in a rare blast of temper, threw the glass of water in his son's face.

He and Mary brought their son to a therapist. "I'm at war with my parents over who is in control," Bill Gates recalls telling the counselor. Reporting back, the counselor told his parents that their son would ultimately win the battle for independence, and their best course of action was to ease up on him.

Mr. Gates Sr. understood that counsel because of his own childhood, an hour's ferry ride from Seattle in the working-class town of Bremerton. "There wasn't a lot of structure to my growing up," he says. "I had an awful lot of discretion about where I went, what I did, who I did it with."

His mother was doting and easygoing. His sister, his only sibling, was seven years older. And his father was a workaholic who sacrificed child-rearing to work at a furniture store he owned with a partner. "His complete focus was on the store," Bill Sr. says.

Mr. Gates Sr. early on built a life outside of his home. Next door, the Braman family had two boys for him to play with and a father who would become his most important role model.

That man, Dorm Braman, had built his business and would later become a Naval officer, mayor of Seattle and a U.S. assistant secretary of transportation. In the late 1930s, Mr. Braman brought Bill Sr. on family road trips across the country. He was scoutmaster of Bill Sr.'s Boy Scout troop, leading the boys on hikes through the Olympic Mountains and driving them in a beat-up bus to Yellowstone and Glacier National Parks. The troop spent two years building a log house from Douglas firs they felled themselves. Mr. Braman had "no sense of personal limitations whatsoever," says Mr. Gates Sr.

Bill Sr. and Mary ultimately took a page from that upbringing: They backed off. They enrolled their son in a school that they thought would give him more freedom. That was the private Lakeside School, now known as the place where Bill Gates discovered computers.

Mr. Gates says he began to realize, "'Hey, I don't have to prove my position relative to my parents. I just have to figure out what I'm doing relative to the world.'"

A Rare Independence

From age 13, he was given rare independence. He took off some nights to enjoy free use of the computers at the University of Washington. He spent chunks of time away from home -- much as his dad had done as a kid. He lived for a time in Olympia, where he was a page in the state legislature, and in Washington, D.C. as a Congressional page. During his senior year, he took a break from school to work as a programmer at a power plant in southern Washington. And in what would become his first major collaboration with Paul Allen, his future Microsoft cofounder, Mr. Gates designed the "Traf-O-Data", a device for counting cars traveling over a section of road.

His parents played supporting roles. They acquiesced when Bill quit Harvard and then moved to Albuquerque, New Mexico, to start Microsoft. It was a tough decision to back.

"Mary and I were both concerned about it -- I think she a bit more than I," Bill Sr. says. "Her expectations and mine were very ordinary expectations of people who have kids in college -- that they get a degree."

The family support was one reason Mr. Gates decided to move Microsoft to Seattle, where he settled into a house not far from his parents. Ms. Gates arranged to have a maid clean her son's house, and made sure he had clean shirts for his big meetings. She also insisted he kept observing the family traditions, including the weekly Sunday dinner at his parents' house.

Mr. Gates Sr., drawing from his own experience as a lawyer guiding small companies, helped find Seattle businesspeople to serve on the Microsoft board. In 1980, Bill Gates brought his father along to dinner to help persuade college friend Steve Ballmer -- now Microsoft's chief executive -- to quit graduate school and join Microsoft. The father's law firm would also end up representing Microsoft, which became the firm's biggest client.

Bill Sr. eased his son's worries about taking Microsoft public when Bill fretted that it would be a distraction for employees. The offering would turn Bill Gates into a billionaire. It also spawned the next challenge for the family.

The Philanthropy Push

After the windfall, Ms. Gates pressed her son to get into philanthropy. At his father's law office late one night, someone present recalls, Bill quarreled with his mother as she urged him to give money away.

"I'm just trying to run my company!" he snapped, says the person in the office at the time. Mr. Gates says that at the time he wasn't opposed to philanthropic work, he just didn't want to be distracted from his duties at Microsoft.

Eventually, she got her son to start a program at Microsoft to raise money for the United Way. He also followed his mother onto the national United Way board in the 1980s.

But as Bill Gates's wealth grew, letters from Seattle-area nonprofits asking for donations piled up. He says he planned to get serious about philanthropy after retiring from Microsoft, or at about 60 years old.

That plan would be fast-tracked after Ms. Gates was diagnosed with a rare form of breast cancer. As she battled the disease, she continued to urge her son to do more philanthropy. Ms. Gates passed away in June 1994.

The day of her funeral, the Gates family had dinner at home. Bill Sr. told his children not to worry about him, saying that he had about 10 good years left in him. He was 70 at the time. Still, after his wife died he was listless.

About six months later, standing in a line for a movie with his son and daughter-in-law, Melinda, the elder Mr. Gates again broached the idea of philanthropy. He suggested he could start sifting through the requests for money and give some out.

A week later, the software mogul set aside about $100 million to create a foundation that his father could run. Bill Gates Sr. later sat at his kitchen table and wrote the first check, $80,000 to a local cancer program.

In the early days, Mr. Gates Sr., who soon remarried, would scribble a few notes on the most-promising requests for donations. He would then put them in a cardboard wine box that he periodically sent to his son's house. The box would come back with the younger Mr. Gates's responses. Mr. Gates Sr. would then reply to all the grant seekers, sometimes including a $1 million check with little more than a single-page letter of congratulations.

Bill Sr. and a former Microsoft executive managed the foundation, doling out money, overseeing a staff of hundreds and expanding its purview to areas like education and vaccines.

Mr. Gates Sr. says he hasn't lost sight of the fact that he was playing the role of caretaker until his son and daughter-in-law took the helm. And after 53 years, he knows to give his son space.

"He has very fixed ideas of some things," says Mr. Gates Sr. "The dynamic of the family is that you don't cross him on those things, because it's a waste of time."

Write to Robert A. Guth at rob.guth@wsj.com