Mike "Twin" Sullivan (September 23, 1878 – October 31, 1937) was an American boxer frequently credited with taking the Welterweight Championship of the World on April 23, 1907 when he soundly defeated William "Honey" Mellody in Los Angeles in a twenty-round bout. He vacated the title in the late fall of 1908, when he could not make weight. Many, though not all sanctioning bodies active today recognize his claim to the title during this period.