The Buffalo Bisons were actually a MLB team in the late 1800s. They were a National League from 1879-1885. The team first became involved in minor league baseball in 1886, after they were dropped from the National League. They stayed there until 1899 when they joined the Western League and were thought of as a real possibility to become a major league baseball team when it was announced that the Western League was becoming the American League. However, they were dropped to make room for another team and returned to minor league baseball again. They would remain in Buffalo until the 1970 season. The team moved to Winnipeg, then Virginia, before they ceased existence after the 1973 season.
The Pittsburgh Pirates brought the Buffalo Bisons back for the 1979 season, making them their AA club. They remained the AA affiliate for the Pirates through the 1982 season, when they took over as the AA club for the Cleveland Indians. After spending 1983 and 1984 as the Indians AA team, the Bisons moved to the American Association as the AAA farm team of the Chicago White Sox. They have been a AAA team ever since. The Bisons were the AAA affiliate of the White Sox for 1985 and 1986, then held the same position for the Cleveland Indians for the 1987 season. After that, they returned to the Pirates organization, this time as the AAA team. They remained there from 1988-1994. Buffalo went back to the Indians organization for the 1995 season, and remained there until 2008. The American Association folded after the 1997 season and the Bisons joined the International League for the 1998 season, where they have been ever since. The Mets owned the Bisons for the next four seasons, and now they are the property of the Blue Jays.
They Bisons have been League Champions 6 times. They beat Rochester in 1934, Baltimore in 1936, Miami in 1957, Rochester again in 1961, Durham in 1998 and Richmond in 2004. They played in a total of 10 Championship Series and since 1998, have won their division 4 times.