ESPN's Bob Ley, who has been a fixture at the network since its launch 40 years ago, announced his retirement on Wednesday.

The 64-year-old Ley made the announcement on social media. He tweeted that he's enjoying the "best of health" and that the decision to retire was "entirely" his own.

"I feel good about it. It is the right decision at the right time in my life, for the right reasons," he said during an appearance on "Outside the Lines," the show he anchored from its launch in 1990 until last year, when he left on a sabbatical.

Ley was ESPN's longest-tenured anchor, joining "SportsCenter" on the channel's third day of operation on Sept. 9, 1979.

"If there is a single word to describe all that Ley contributed, all the ways in which he helped build ESPN, it would simply be integrity," host Jeremy Schapp said during an "Outside the Lines" segment recapping Ley's career.

ESPN president Jimmy Pitaro said Ley set "the standard of excellence" with his "unwavering commitment and unparalleled work ethic."

Ley hosted the first NCAA selection show and the inaugural live broadcast of the NFL draft in 1980. He also anchored many of sports biggest news stories over the past 40 years, including the Boston Marathon bombing and the death of Muhammad Ali.

He also provided the first live national reports during the earthquake in San Francisco at the 1989 World Series.

The investigative program "Outside the Lines" will be Ley's legacy at the network. It started as a series of specials, became a weekly show in 2000 and then began airing daily three years later.

On "Outside the Lines," Ley led reporting on concussions and the NFL's handling of domestic violence cases. The show also gave extensive coverage to the Jerry Sandusky sexual abuse findings at Penn State, which resulted in the resignation of coach Joe Paterno, and former U.S. gymnastics doctor Larry Nassar's history of sexual abuse.

"Outside the Lines" has received four Edward R. Murrow Awards and two Peabody Awards.

"Bob Ley has always been ESPN's North Star. From the moment we went on the air 40 years ago until right now, he has guided us in the right direction. He has kept us honest," NFL studio host Chris Berman said in a statement.

Ley, who won 11 Sports Emmy Awards, was inducted into the National Sports Media Association Hall of Fame this week. He said he plans to work with Seton Hall University, his alma mater, in retirement.

Ley said he was proud to be a part of ESPN, as well as building "Outside the Lines" and his coverage of soccer.

"I'm proudest of being at the ground floor of something that has become an American cultural institution," he said. "I don't think you can write the cultural history of the United States over the past 40 years without being a chapter on sports and this entity, which is now a global model."

— Associated Press