He is in his 20th season at the helm of the Oakland A’s, has been the subject of a best-selling book and Academy Award-nominated movie, and is recognized beyond the world of sports for his innovative mind.

So is Billy Beane’s legacy established? Or must the A’s executive win a championship or three, as the Bay Area’s other longtime top baseball executive has done, to solidify his place in the sport?

“First and foremost, in Billy’s organization and amongst his brethren in baseball, nothing is lost when it comes to his success and how he goes about his business,” Giants Executive Vice President of Baseball Operations Brian Sabean said. “The fact Billy doesn’t have a World Series ring ... Lord knows, he’s an icon in his organization and among his peers. Everyone knows Billy and what he’s done. That’s the ultimate compliment.”

Beane, 55, is best known for the outside-the-box thinking highlighted in “Moneyball” — identifying undervalued assets as a means to make a low-payroll club competitive with the big boys. The book is required reading at nearly every business school, making Beane an icon in boardrooms and greatly in demand on the corporate public-speaking circuit.

His teams have made the postseason eight times since he took over Oakland’s front office in 1998 — including the 2002 season that “Moneyball” chronicled, a trip to the American League Championship Series in 2006, and a three-year boon kick-started by an out-of-nowhere 2012 team that won the American League West on the final day of the regular season.

But the periods between sometimes have been bleak, no more so than this current stretch that finds the A’s last in their division for the third year in a row.

“The biggest thing is that unless Billy wins a championship — that will be it,” “Moneyball” author Michael Lewis said of Beane’s legacy. “But it’s a huge thing: He made it cool to bring science into player evaluation, and because of that, every businessperson in America wants to meet him.

“When you think of people who’ve had that kind of cultural effect on sports, it’s very few. Branch Rickey breaking the color barrier, really jarring the culture. ... It’s hard to think of anyone else. Billy burst out of baseball the way people in baseball really just don’t.”

An incomplete checklist

Beane downplays any talk about personal accomplishments. Fiercely loyal to the rest of the A’s organization, he considers all successes shared, and he knows the checklist is minus a title.

“The desire for a championship is less for myself than it is for the people who work here and the people in the community,” Beane said. “I’ve never set out for my own personal legacy. I always sort of chuckle over that idea — the only legacy I have any concern about is my children.”

Former A’s Assistant General Manager Farhan Zaidi, now the GM of the Dodgers, flipped around Beane’s sentiments, saying, “People like me who worked for him — we want it more for him than he wants it for himself.”

With Oakland making it out of the first round of the playoffs just once during Beane’s stewardship and at the bottom of the AL West for the third year in a row, there is more scrutiny on the vice president of baseball operations than at any time in the past.

And he is not without his missteps. Fans and columnists alike have taken Beane to task for several decisions that coincided with the start of the team’s current down period.

Top on the list: trading third baseman Josh Donaldson, who went on to be the MVP after going to Toronto, in exchange for four players who have not nearly approached that kind of star power.

“In hindsight, that was certainly questionable — and I’m being kind to myself,” Beane said recently in his first public comments reproaching himself for the deal. “There were a number of reasons why, and Josh was a good player who became a great player — but when you make as many transactions as we do, some are going to be good and some are not going to be good.

“It’s with some mea culpa that that one can be judged. Fair enough.”

Beane acknowledged the disaster that was the three-year, $30 million Billy Butler signing when the under-productive designated hitter was let go last season. But Beane remains firm that trading star outfielder Yoenis Cespedes for pitching ace Jon Lester in mid-2014 was necessary. “Without Jon Lester, we don’t make the playoffs that year,” Beane said.

“I can remember sitting around having heartburn about what we’d given up in a trade and Billy saying, ‘Focus on what we’re getting, not what we’re giving up,’” Zaidi said. “You can’t get burned by the trades you don’t make — but he’s never let that affect him to the detriment of the franchise. The way trades are received — the notion that this is a really smart trade, this is a really dumb trade — Billy’s philosophy doesn’t change from trade to trade, and he’s secure enough to stick with it. He’ll make trades even when they open him up to second guessing, and the more trades you make, the more chances there are to make mistakes. He’s never let that bother him.”

Financial restraint

Given the A’s limited resources, trades are their lifeblood. Oakland annually is among the lowest spenders despite having one of the wealthiest owners in John Fisher. Though Beane owns a small percentage of the team himself, he is not in charge of the budget amount — that comes from majority ownership — but he always has been firmly on board with the idea that the payroll should be based on revenue, not on the owner’s personal fortune.

Beane began his A’s tenure when the free-spending Walter Haas family owned the club, and he loved how the Haases ran things as the team went to the World Series in 1988, 1989 and 1990. But Beane also watched as an ever-ballooning payroll became unsustainable, rocketing from $19.9 million in 1990 to $33.63 million in 1991 as large deals went to stars such as Jose Canseco, who became baseball’s first $5 million - per - year player.

“I became very close to Wally and the Haas family and it was everything everyone perceives it to be, but you saw over the final years it became a financial strain that led to the sale of the team,” Beane said. “Ultimately, doing that without a forecast will come back to get you. If you wait too long, the adjustment is brutal.”

Playoff regulars Toronto and Oakland had two of the top four payrolls in baseball by 1993, but even as the spending took off, the A’s postseason run ended in ’92 and the Blue Jays’ in ’93. Revenue failed to keep up, especially after the 1994-95 strike. It took Oakland eight seasons to make it back; the Blue Jays 22.

“We went 1-2 to the bottom almost immediately,” Beane said. “It’s like landing a jet plane in reverse, it’s very difficult to do. There are some very uncomfortable decisions that have to be made.”

The Haas family sold the club in 1995. Lesson learned, as far as Beane was concerned.

When he succeeded influential General Manager Sandy Alderson in 1998, Beane was sold on financial restraint, and major free-agent deals were no longer the norm. Wheeling and dealing would supplement the roster, instead, and Beane became a bold practitioner.

“In this market, I believe if you become paralyzed by fear, you’re done,” he said. “You can make decisions that aren’t good — but you can never not make a decision because of fear. So much of running this organization is the financial limitations. I know people are tired of hearing it, but it’s a fact.

“Because I have my hands on the largest line item in our budget, I’ve always felt it’s my responsibility to live within our means in order to run the business — and it should be based on the business’ revenue. Funding on revenues is the only way it will work. There may be a time for deficit spending, there will be a time for investment, but you want to make sure you’re doing it correctly.”

The road ahead

Oakland is gradually losing its hold on revenue-sharing, the system Major League Baseball uses to redistribute income from richer teams to poorer teams. The three-year phase out will cost the team more than $35 million by 2020. The best and really only hope to boost revenue is a new ballpark, and the team has said a stadium site will be announced this year.

With the potential for a bigger budget to stock a new ballpark with a winning team, Beane might, for the first time in his career, be able to wrap up a number of key players to long-term deals. He would have liked to do it earlier, lamenting that the team didn’t have the wherewithal to keep any of the players from the early 2000s teams except Eric Chavez.

“It was really unique to have that kind of talent on one team, and it was organic,” Beane said. “But you look at those players and how long many of them played beyond that, and you realize the frustrations of not fulfilling everything. You understand the fans’ dissatisfaction. Keeping players like that is one thing we haven’t been able to do, and what we’re hoping we will be able to do here soon.”

The A’s current project with a number of good, young position players is right up Beane’s alley. He enjoys the challenges of reformulating teams even more than the winning seasons. That’s how he made his name, after all — finding ways to put together contenders even without a large payroll.

“Looking back, the most satisfying part of the job is watching something successful take shape,” Beane said. “This year, you see Matt Chapman and Matt Olson, Chad Pinder, you watch the growing process. One good day, one bad day, then it’s two good days and one bad day. That’s really why a lot of us are in the game, at heart that’s what most of us love. And if fans see the vision, they get excited. If you look up and don’t see anything better on the horizon, I understand that frustration.”

Few pro sports executives last as long as Beane and Sabean, so the question is: Will Beane be around to enjoy his most recent rebuild? Or a new stadium? His contract runs through 2019 and, while Beane is happy in his position, those who know him well always have suspected that at some point he will want to pursue other challenges.

“I do like the direction we’re going in, and that’s still the most exciting part of the job,” Beane said. “And as long as I find the job exciting and rewarding, I’ll want to do it.”

Susan Slusser is a San Francisco Chronicle staff writer. Email: sslusser@sfchronicle.com Twitter: @susanslusser

Billy Beane

Age: 55

Born: Orlando

High school: Mt. Carmel (San Diego)

MLB draft: 1st round (23rd overall) by New York Mets in 1980

Playing career : 6 years in MLB

Overall record as A’s top baseball executive: 1,678-1,527

Highlights: 6 division titles, 8 playoff appearances

What his peers say

His legacy is that he’s one of the great minds of baseball, period. That’s something you can’t deny, playing in a small market and making enough noise not just to be relevant but to be feared.

— Brian Cashman, New York Yankees general manager

Billy has challenged everyone in the industry to examine different ways of evaluating players, putting together front office staffs and scouting staffs, coaching staffs. He’s a very flexible thinker and he tends to explore untapped territory; when other people focus on one area, he has the instincts to go to other areas.

— Dayton Moore, Kansas City Royals general manager

It’s always impressive when someone holds a key leadership position for 20 years or more; that’s a real talent and an ability to lead an organization for a long period, through a lot of changes.

— Jeff Luhnow, Houston Astros general manager