Donald David Dixon Ronald O’Connor (August 28, 1925 – September 27, 2003) was an American dancer, singer, and actor who came to fame in a series of movies in which he co-starred alternately with Gloria Jean, Peggy Ryan, and Francis the Talking Mule. He is best known today for his role as Don Lockwood's friend and colleague Cosmo Brown in Singin' in the Rain (1952).