Frederick Mitchell Walker (March 21, 1884 – February 1, 1958), nicknamed "Mysterious", was an American athlete and coach. He was a three-sport athlete for the University of Chicago from 1904 to 1906 and played Major League Baseball as a right-handed pitcher for the Cincinnati Reds, Cleveland Indians, Brooklyn Superbas, Pittsburgh Rebels and Brooklyn Tip-Tops.He earned the nickname "Mysterious" after pitching under a pseudonym for the San Francisco Seals of the Pacific Coast League in 1910.