The team announced his passing Sunday, writing ... "There are few players with a more decorated career than Vida Blue. He was a three-time champion, an MVP, a six-time All-Star, a Cy Young Award winner, and an Oakland A's Hall of Famer."

The A's add ... "Vida will always be a franchise legend and a friend. We send our deepest condolences to his family and friends during this arduous time." No other details about a cause of death were released -- the condolences, however, are pouring in from all over.

The man certainly left a mark on the game. As the A's noted, he'd won three World Series with the team in '72, '73 and '74 ... serving as an integral part of the starting rotations during their five years of dominance in baseball. And, as they note ... he was voted in as the best pitcher in the American League during his breakout year with the A's in 1971.

His stats, at times, were off the charts ... once achieving a 1.82 ERA in a season -- which means people weren't getting very many hits off him. He was a southpaw pitcher, and Vida had nasty stuff for that era. By and large, he was considered a massive threat on the mound.

VB was also known for his shrewd business savvy behind the scenes. He famously locked horns with the A's ownership for a big bump in salary -- and he ultimately got it.

Like we mentioned, just about every organization tied to MLB is sending a tribute to the guy ... which speaks to his impact. In addition to playing for the A's, Vida was also on the SF Giants and the Kansas City Royals before he retired in 1987. Vida was also a 6-time All-Star and the American League MVP in 1971 ... on top of all his other accolades.