"Razor" Robert Alexander 'Rob' McCullough IV (born May 26, 1977) is an American Muay Thai fighter and mixed martial arts (MMA) fighter. He was a five-time World Muay Thai champion, and is a former World Extreme Cagefighting (WEC) lightweight champion. He is now currently back in Irvine training under Coach Colin Oyama.

McCullough defeated Muay Thai fighter Kit Cope at WEC 25 to take over the vacant WEC lightweight title. On February 13, 2008, he lost his title to Jamie Varner when Varner defeated him by TKO due to strikes in the third round.