WASHINGTON (AP) — Former U.S. Solicitor General Ted Olson, who served two Republican presidents as one of the country’s best known conservative lawyers and successfully argued on behalf of same-sex marriage, died Wednesday. He was 84.

The law firm Gibson Dunn, where Olson practiced since 1965, announced his death on its website. No cause of death was given.

Olson was at the center of some of the biggest cases of recent decades, including a win on behalf of George W. Bush in the 2000 Florida presidential election recount dispute that went before the U.S. Supreme Court.

“Even in a town full of lawyers, Ted’s career as a litigator was particularly prolific,” said Mitch McConnell, the longtime Senate Republican leader. “More importantly, I count myself among so many in Washington who knew Ted as a good and decent man.”

Bush made Olson his solicitor general, a post the lawyer held from 2001 to 2004. Olson had previously served in the Justice Department as an assistant attorney general during President Ronald Reagan’s first term in the early 1980s.

During his career, Olson argued 65 cases before the high court, according to Gibson Dunn.

One of Olson’s most prominent cases put him at odds with many fellow conservatives. After California adopted a ban on same-sex marriage in 2008, Olson joined forces with former adversary David Boies, who had represented Democrat Al Gore in the presidential election case, to represent California couples seeking the right to marry.

A federal judge in California ruled in 2010 that the state’s ban violated the U.S. Constitution. The U.S. Supreme Court let that decision stand in 2013.

“This is the most important thing I’ve ever done, as an attorney or a person,” Olson later said in a documentary film about the marriage case.

He told The Associated Press in 2014 that the marriage case was important because it “involves tens of thousands of people in California, but really millions of people throughout the United States and beyond that to the world.”

Barbara Becker, managing partner of Gibson Dunn, called Olson “creative, principled, and fearless”

“Ted was a titan of the legal profession and one of the most extraordinary and eloquent advocates of our time,” Becker said in a statement.