William George Bonin (January 8, 1947 – February 23, 1996), also known as the Freeway Killer, was an American serial killer and twice-paroled sex offender who committed the rape, torture, and murder of a minimum of twenty-one young men and boys in a series of killings in southern California from May 1979 to June 1980. On at least twelve occasions, Bonin was assisted by one of his four known accomplices; he is also suspected of committing a further fifteen murders.

Described by the prosecutor at his first trial as "the most arch-evil person who ever existed", Bonin was convicted of fourteen of the murders linked to the "Freeway Killer" in two separate trials in 1982 and 1983. He spent fourteen years on death row before he was executed by lethal injection at San Quentin State Prison in 1996. Bonin was the first inmate in California to die by this method.

Bonin became known as the "Freeway Killer", as well as the Freeway Strangler, due to the fact that the majority of his victims' bodies were discovered alongside numerous freeways in southern California. He shares this epithet with two separate and unrelated serial killers active in and around southern California in the 1970s: Patrick Kearney and Randy Kraft.