Weaver managed the Orioles from 1968-1982 and in 1985-1986. His team won the World Series in 1970.
"Earl Weaver stands alone as the greatest manager in the history of the Orioles organization and one of the greatest in the history of baseball," Orioles managing partner Peter Angelos said in a written statement. "This is a sad day for everyone who knew him and for all Orioles fans."
Weaver was participating in an off-season cruise for Orioles fans when he was stricken by an apparent heart attack. He had been scheduled to take part in the team's annual Fan Fest in Baltimore Saturday, The Baltimore Sun said.
"It's a sad time, but at the same time, Earl would say I hope it won't mess up FanFest," Orioles Manager Buck Showalter told fans. "Every time I look at an Oriole now, it's going to be missing a feather without Earl."
Funeral arrangements were pending.
Weaver racked up a 1,480-1,060 record with the Orioles and managed Baltimore legends such as Jim Palmer, Cal Ripken, Brooks Robinson, Frank Robinson and Eddie Murray. With Weaver as their skipper, the Orioles won six division titles and four pennants, along with the series title. He was elected to the Hall of Fame in 1996.
His success on the field was matched by his outsized on-field persona, which included volcanic eruptions aimed at umpires whose calls had irked him. The Sun said Weaver once said he wanted his epitaph to read, "The sorest loser that ever lived."
He was ranked first among managers with an average of 94.3 victories per season, and his .583 winning percentage was 10th among all managers.
"I'm very humble to go into the Hall of Fame, where there are four Baltimore Orioles whom I managed, Brooks Robinson, Frank Robinson, Reggie Jackson and the man I had more arguments with than with my wife, Marianne, Jim Palmer," said Weaver. "I'm proud of my record and proud that I was even considered for election and I proud that I spent my entire career in one city Baltimore. I'm proud the wonderful fans of Baltimore kept me around."
Weaver spent 20 years in the minor leagues as a player and manager and never was a player in the major leagues. He became the Orioles manager in 1968 when Hank Bauer was fired during the all-star break, and managed in the days before the club drew large crowds or paid big salaries. His last season was in 1982.
He was the Orioles manager who started Ripken at third base as a rookie then moved him to shortstop. Despite Ripken's less-than-spectacular rookie start 4 for 55 and a batting average of .177 Weaver constantly assured the young player that he would not be sent back to the minors. When Ripken became the club's shortstop, he started at the position for more than 13 years, beating Lou Gehrig's consecutive game record in 1995.
Weaver was only the 13th manager to get into the Hall of Fame, joining legends Walter Alston and Casey Stengel. He spent all of 17 seasons with the Orioles and had only a single losing season in 1986 when the club's farm system collapsed.
Known among his players for his habit of cussing them out loudly and angrily whenever he felt they had miscued or played badly, Weaver argued often with umpires over errant calls and was ejected more than any other manager. At his induction, however, he praised the game's umpires and said," They made a million calls when I was there and, except for the 91 or 92 times I disagreed, they got them right."
Weaver was born Aug. 14, 1930, in St. Louis, the son of Earl Milton and Ethel Weaver. His second marriage was to Marianne Osgood on Sept. 16, 1964. He had three children by a previous marriage and another child with his second wife.