The Louisville Colonels were a Major League Baseball team that also played in the American Association (AA) throughout that league's ten-year existence from 1882 until 1891. They were known as the Louisville Eclipse from 1882 to 1884, and as the Louisville Colonels from 1885 to 1891; the latter name derived from the historic title of the Kentucky Colonel. After the AA folded in 1891, the Colonels joined the National League and played through the 1899 season.

Major League Baseball (MLB) is a professional baseball league and the highest level of organized baseball in the United States and Canada. One of the big four major leagues, MLB comprises 30 teams, divided equally between the National League (NL) and the American League (AL), with 29 in the United States and 1 in Canada. Formed in 1876 and 1901, respectively, the NL and AL cemented their cooperation with the National Agreement in 1903, making MLB the oldest major professional sports league in the world. They remained legally separate entities until 2000, when they merged into a single organization led by the Commissioner of Baseball. MLB is headquartered in Midtown Manhattan.