Jack Hammer is the pseudonym of Troy Mainwaring, born 10 November 1963 in Los Angeles, California, an American male actor in pornography.

He is a muscular man with brown hair. He wears many tattoos, including a cross and a skull. He often performs in interracial pornography and gang bangs. Though he mostly performs with women, he has also worked in transsexual pornography and bisexual pornography. He has appeared in over 300 titles.

Hammer began his pornographic career in the summer of 1995, after being paroled from prison after serving five years for armed robbery. His marriage to pornographic film actress Sweety Pie dissolved among allegations of his threatening and assaulting her, which caused him to be jailed for violating parole. In October 2001, he was sentenced to another year for leaving threatening messages for an HBO documentary producer. He was still, or again, in a California prison as of October 10, 2005.