Louis Graydon Sullivan (June 16, 1951 – March 2, 1991) was an American author and activist known for his work on behalf of trans men. He was perhaps the first transgender man to publicly identify as gay, and is largely responsible for the modern understanding of sexual orientation and gender identity as distinct, unrelated concepts.Sullivan was a pioneer of the grassroots female-to-male (FTM) movement and was instrumental in helping individuals obtain peer-support, counselling, endocrinological services and reconstructive surgery outside of gender dysphoria clinics. He founded FTM International, one of the first organizations specifically for FTM individuals, and his activism and community work was a significant contributor to the rapid growth of the FTM community during the late 1980s.