The Famous Chicken, also known as the San Diego Chicken, was a mascot originally created by KGB radio in San Diego for station promotions. Eventually the station and Ted Giannoulas, the man who inhabited the costume, parted in a dispute and Giannoulas had the character “re-hatched” in a 1979 promotion in San Diego.
If you attended MLB games in the 1980s you likely saw him perform. He’d do 250+ appearances a year in those days; later, when teams created their own mascots — in large part because of the Chicken’s popularity — he wound up appearing at a lot of minor-league games.