Former major league pitcher Matt Keough, a special assistant with the Oakland Athletics, has died, the team announced on Saturday. He was 64.

The A's did not disclose details on the cause of death.

Keough spent parts of seven seasons with Oakland as a player, ending in 1983, and was named an All-Star as a rookie in 1978. He was also was honored with the American League Comeback Player of the Year award in 1980, and pitched for the Yankees, Cardinals, Cubs and Astros as well.

"Matt was a great baseball man and a proud Oakland A," executive vice president of baseball operations Billy Beane said in a statement. "He had an incredible passion for the game and we were lucky to have him and his wealth of knowledge alongside us for the years he worked as a special assistant."

The A's organization mourns the loss of former pitcher and special assistant Matt Keough.

"He left an unforgettable impression on everyone he touched in baseball. Our sincere condolences are with the entire Keough family tonight." - Billy Beane pic.twitter.com/sEGaLiFLc7

— Oakland A's (@Athletics) May 3, 2020

After retiring as a player, he graduated to on-field and front-office roles with the Angels and Rays, in addition to the Athletics. The 6-foot-3 right-hander finished with a record of 58-84, with a 4.17 ERA, a 1.43 WHIP and 590 strikeouts in 215 games.

Keough was part of an impressive Oakland rotation known as the "Five Aces," which also included Rick Langford, Steve McCatty, Brian Kingman and Mike Norris. The "Aces" graced the cover of Sports Illustrated in 1981.

"He left an unforgettable impression on everyone he touched in baseball," Beane said.

Keough's best year came in 1980, when he went 16-13 for the Athletics, sporting a 2.92 ERA in 32 starts, with a career-high 121 strikeouts.