T. Boone Pickens, the billionaire oil tycoon whose money helped put Oklahoma State football on the map, died Wednesday. He was 91.

Pickens had been battling a series of strokes and head injuries as a result of a fall he took in 2017, according to his spokesman, Jay Rosser.

Pickens' penchant for philanthropy and love for Oklahoma State football dovetailed in 2006 when he donated $165 million to the athletic program, the largest single gift in NCAA history.

"The greatest Cowboy of them all has taken his last ride," athletic director Mike Holder said in a statement. "It will never be the same again. We could never thank him enough for all that he did for our university. He gave us everything he had -- and all that he asked in return was that we play by the rules and dream big. He was living proof that anything is possible if you're wearing orange. 'Great ride Cowboy, great ride!'"

Pickens graduated from Oklahoma State in 1951 with a degree in geology when the university still went by Oklahoma A&M.

He wound up giving more than $300 million to Oklahoma State athletics.

Pickens' initial contribution bankrolled several state-of-the-art athletic facilities, as well as a new football stadium, which was named after him.

"I know how to win. I have won before. And I win every day in the business I am in," Pickens told ESPN in 2006. "I don't find sports a helluva lot different than business. ... I want us to be competitive."

With sparkling facilities to attract recruits, that's exactly what Oklahoma State football became under Mike Gundy, whom Pickens had urged Holder to promote to head coach after Les Miles left for LSU in 2004.

Gundy paid tribute to Pickens on Twitter.

Mr. Pickens is a big part of our success and we're all thankful for the lasting impact he's had on Oklahoma State. It would have been difficult for us to climb as high as we have without him. He'll be missed, but his legacy here will live on for a long time to come. pic.twitter.com/1jYVwBcHo0

— Mike Gundy (@CoachGundy) September 11, 2019

Before Pickens' donation, the Cowboys had reached double-digit wins only three times in their history. Since, they've won 10 or more games in six seasons. In 2011, Oklahoma State captured its first Big 12 title and just narrowly missed out on playing LSU for the BCS National Championship.

"We have some added advantages that we've never had," Gundy said in 2008, when his team climbed into the top 10 of the polls for the first time since Barry Sanders' Heisman Trophy season in 1988. "It would have never happened without [Pickens]. There's just no way. It couldn't happen."

Yet as Oklahoma State rose to prominence behind Pickens' and Gundy's contributions, tensions rose between them. Pickens would become irritated when Gundy entertained job overtures. And on multiple occasions, Pickens publicly criticized Gundy for having a poor record against rival Oklahoma.

But in 2017, the two made amends, and Pickens tweeted a letter of support to Gundy after Oklahoma State's 62-52 loss to the Sooners.

"Over the years, him and I have butted heads a lot, but we do think a lot alike and we have a common goal," Gundy said a week later. "He wants to win every game. He's a competitor."

Pickens made his fortune founding Petroleum Exploration with just $2,500 in 1956. Over the following three decades, the company he renamed Mesa Petroleum ballooned into one of the largest oil companies in the world. Pickens later became famous for being a corporate raider of other oil companies. In 1985, Time magazine put him on its cover with the headline "The Takeover Game."

At 68, Pickens left Mesa and founded the hedge fund BP Capital Management, which bet heavily and successfully on natural gas, turning him into one of the richest people in America, while laying the groundwork for his involvement in Oklahoma State athletics.

"He was the ultimate Cowboy,'' Oklahoma State University president Burns Hargis said in a statement. "It is impossible to calculate his full impact on Oklahoma State. His historic gifts to academics and athletics not only transformed the university, they inspired thousands of others to join in the transformation.''

Pickens was born Thomas Boone Pickens Jr. on May 22, 1928, in Holdenville, Oklahoma. After graduating from high school in Amarillo, Texas, Pickens spent one year at Texas A&M on a basketball scholarship. When that scholarship was not renewed, he transferred to Oklahoma A&M.

Pickens was married and divorced five times. He is survived by five children and 11 grandchildren.