Hagy was found unresponsive in his home by his roommate, the Orioles said. Efforts by paramedics to revive him failed.
Wearing a straw hat and a scraggly beard, Hagy led cheers at the Orioles' old stadium during the 1970s and 1980s. He spelled out O-R-I-O-L-E-S with his body while fans yelled each letter in unison.
"He was part of a great era," Orioles Hall of Fame pitcher Jim Palmer said. "If you recall, we didn't draw many people back then. Best team in baseball, and we were drawing 1.2 million. He made it exciting to come to the ballpark."
A cabdriver during the day, Hagy guzzled many a beer in the stands while the fans eagerly waited for him to wave his hands over his head to start his trademark cheer. During important games, the team allowed him to climb on top of the Orioles dugout to rally the crowd with his act.
"It was nice to have an unofficial, official cheerleader," Palmer said.
Asked to explain how the phenomenon began, Palmer jokingly replied, "I don't know if he picked up (owner) Jerry Hoffberger at the train station in his cab. I just know for a team that didn't draw very well, it was very refreshing that he actually came out to the ballpark and generated not only fans, but interest in the team. He loved the Orioles."
Hagy was scruffy, had a beer belly and often wore tank tops to the game. Yet this cabdriver from Dundalk led a generation of Orioles backers in the cheap seats of an aging stadium that drew far more fans for NFL games involving the Baltimore Colts.
"If you go back and look at history of Baltimore, we were always kind of on the other side of the tracks," Palmer said of the Orioles. "When I first came to Baltimore, you had Washington and then you had Baltimore. So, I thought he was somebody you could relate to. People loved to sit up there."
Hagy put an end to his antics when the Orioles moved to Camden Yards in 1992, in part because he couldn't stand the new breed of upper-crust fans who spoke on cellphones during the game. But he reprised his act in the middle of the decade during the playoffs.