Nearly a decade ago, I read a story in Fortune about Silicon Valley’s best kept secret. It wasn’t a piece of hardware or a bit of software. It wasn’t even a product. It was a man. His name was Bill Campbell, and he wasn’t a hacker. He was a football coach turned sales guy. Yet somehow, Bill had become so influential that he went on a weekly Sunday walk with Steve Jobs and the Google founders said they wouldn’t have made it without him.

Bill’s name sounded familiar, but I couldn’t place it. Eventually it hit me: I recognized him from a case I had taught a few times on a management dilemma at Apple in the mid-1980s, when a brave, bright young manager named Donna Dubinsky challenged a distribution plan from Steve Jobs himself. Bill Campbell was Donna’s boss’s boss, and he dished out exactly the kind of tough love you’d expect from a football coach: he tore her proposal apart, pushed her to come up with something stronger, and then stood up for her. I hadn’t heard of him since—the next few decades of his career were a mystery.

The story gave me a clue about why: Bill loved shining the spotlight on others but preferred to stay in the shadows himself. I was writing a book on how helping others can drive our success, and it dawned on me that he would be a fascinating character to profile. But how do you profile someone who shuns public attention?

I started by cobbling together everything I could find about him online. I learned that what Bill lacked in physical strength he made up in heart. He was the MVP of his high school football team despite standing 5’10” and weighing 165 pounds. When the track coach was short on hurdlers, Bill volunteered. Since he couldn’t jump high enough to clear the hurdles, he just ran right through them, bruising himself all the way to the regional championships. In college he played football at Columbia, where he was elected captain, and went on to become the head coach there, struggling through six straight losing seasons. His Achilles heel? He cared too much about his players. He was reluctant to bench walk-ons who gave it their all and refused to ask his stars to put sports above school. He was there to make his players successful in life, not on the field. He was more interested in their well-being than in winning.

When Bill decided to transition to business, it was his old football teammates who opened the door. They were convinced that his weakness in a zero-sum sport could be a strength in many companies. Sure enough, Bill ended up excelling as an executive at Apple and as the CEO of Intuit. Every time I talked to someone in Silicon Valley who had a reputation for unusual generosity, they told me the same thing: it was Bill Campbell who gave them their worldview. Not wanting to bother Bill himself, I started reaching out to his mentees. Soon I had a flurry of calls with Bill’s protégés, who described him as a father and compared him to Oprah. The calls usually ended with me scribbling down a dozen new names of people whose lives Bill had changed. One of those names was Jonathan Rosenberg.

When I got in touch with Jonathan in 2012, he took the liberty of copying Bill himself on the email thread. Bill declined to be featured, closing the door on that chapter of my book—and on my quest to find out how he had done so much good for others while doing great for himself as well. Ever since, I’ve wondered how he flourished as a giver in a field that supposedly rewards takers, and what we could learn from him about leadership and management.

I’m delighted to say that at long last, thanks to Trillion Dollar Coach, I have my answers. The book reveals that to be a great manager, you have to be a great coach. After all, the higher you climb, the more your success depends on making other people successful. By definition, that’s what coaches do.

For the past ten years, I’ve had the privilege of teaching the core teamwork and leadership class at Wharton. The course is based on rigorous research, and I’m struck by how brilliantly Bill Campbell anticipated the evidence. He was living theories in the 1980s that experts didn’t even develop (let alone validate) until decades later. I was also taken aback by how many of Bill’s insights around managing people and coaching teams are still ripe for systematic study.

Bill was ahead of his time. The lessons of his experience are timely in a collaborative world, where the fates of our careers and our companies hinge on the quality of our relationships. But I believe they’re also timeless: Bill’s approach to coaching would work in any era.

Coaching is in vogue: it used to be just athletes and entertainers who had coaches, but now we have leaders taking on executive coaches and employees learning from speaking coaches. The reality, though, is that a formal coach will only see a fraction of the moments where you could benefit from feedback and guidance. It’s up to all of us to coach our employees, our colleagues, and even sometimes our bosses.

I’ve come to believe that coaching might be even more essential than mentoring to our careers and our teams. Whereas mentors dole out words of wisdom, coaches roll up their sleeves and get their hands dirty. They don’t just believe in our potential; they get in the arena to help us realize our potential. They hold up a mirror so we can see our blind spots and they hold us accountable for working through our sore spots. They take responsibility for making us better without taking credit for our accomplishments. And I can’t think of a better role model for a coach than Bill Campbell.

I don’t make that statement lightly. I’ve had the chance to learn up close from some elite coaches—not just in business, but in sports too. As a springboard diver, I trained under Olympic coaches, and more recently as an organizational psychologist, I’ve worked with great coaches like Brad Stevens of the Boston Celtics. Bill Campbell doesn’t just belong in that elite group of world-class coaches. He invented his own category, because he could coach people doing work he didn’t even understand.

In 2012, the same year that I gave up on writing about Bill, I was invited to give a talk at a global Google event on how I would run the company as an organizational psychologist. Having worked for a few years with Google’s pioneering people analytics team, it became obvious to me that almost everything great in the company happened in teams. That was my pitch in the talk: start treating teams, not individuals, as the fundamental building block of the organization. My Google colleagues did one better: they launched a major study, which they published as Project Aristotle, to identify the distinguishing characteristics of their most successful teams.

The five key factors could have been taken right out of Bill Campbell’s playbook. Excellent teams at Google had psychological safety (people knew that if they took risks, their manager would have their back). The teams had clear goals, each role was meaningful, and members were reliable and confident that the team’s mission would make a difference. You’ll see that Bill was a master at establishing those conditions: he went to extraordinary lengths to build safety, clarity, meaning, dependability, and impact into each team he coached.

It's unfortunate that every bookstore has a self-help section, but there isn’t a help-others section. Trillion Dollar Coach belongs in the help-others section: it’s a guide for bringing out the best in others, for being simultaneously supportive and challenging, and for giving more than lip service to the notion of putting people first.

What’s most remarkable about Bill Campbell’s story is that the more you read about him, the more you’ll see opportunities every day for becoming more like him. There are small choices, like treating everyone you meet with dignity and respect. And there are bigger commitments, like taking the time to show a sincere interest in the lives of your team—to the point of remembering where their kids go to school.

Bill Campbell didn’t need or want the glory of being profiled in a book, let alone being the subject of an entire book. But for a man who lived his life by giving his knowledge away, open-sourcing his secrets strikes me as a fitting tribute.