Lee Harvey Oswald (October 18th, 1939 - November 24th, 1963) was a former U.S. Marine (from October 1959 - June 1962) who had briefly defected to the Soviet Union. There, he studied communism and socialism and married a Russian woman.
Oswald was the one officially blamed for the Assassination of John F. Kennedy, reportedly shooting the 35th U.S. President and killing a police officer named J.D. Tippit approximately 40 minutes later while fleeing. However, he denied involvement in both killings.
There have been many theories about the assassination, some more plausible than others, that he really might have been innocent, or at least didn't act alone in killing JFK. Either way, two days after he committed both murders, Lee Harvey Oswald was murdered by gangster-wannabe Jack Ruby in an act of vigilantism.