Leo Joseph Ryan, Jr. (May 5, 1925 – November 18, 1978) was an American politician of the Democratic Party. He served as a U.S. Representative from the 11th Congressional District of California from 1973 until he was murdered in Guyana by members of the Peoples Temple shortly before the Jonestown Massacre in 1978.

After the Watts Riots of 1965, then-Assemblyman Ryan took a job as a substitute school teacher to investigate and document conditions in the area. In 1970, he experienced life as an inmate in Folsom Prison, while presiding as chairman on the Assembly committee that oversaw prison reform. During his time in Congress, Ryan traveled to Newfoundland to investigate the killing of seals.

Ryan was also famous for vocal criticism of the lack of Congressional oversight of the Central Intelligence Agency (CIA), and authored the Hughes-Ryan Amendment, passed in 1974. He was also an early critic of L. Ron Hubbard and his Scientology movement and of the Unification Church of Sun Myung Moon. On November 3, 1977, Ryan read into the United States Congressional Record a testimony by John Gordon Clark about the health hazards connected with destructive cults.