Wilbur Underhill Jr. (March 16, 1901 – January 6, 1934), often called "Mad Dog" or the "Tri-State Terror", was an American criminal, burglar, bank robber and Depression-era outlaw. He was one of the most wanted bandits in Oklahoma during the 1920s and 1930s and co-led a gang with Harvey Bailey that included many fellow Cookson Hills outlaws including Jim Clark, Ed Davis and Robert "Big Bob" Brady.