October 18, 1939 - November 24, 1963: Age 24
Lee Harvey Oswald's most memorable action in his short life was to shoot President John F. Kennedy. Although there are many alternate theories, four separate government investigations have confirmed that he did indeed point a gun out of the window of the sixth floor at a warehouse and shoot the President (YouTube video) as he was passing by in an open convertible. The Governor of Texas and a passer-by were also wounded.
Oswald enlisted in the Marines a week after his 17th birthday, but by the time he finished his stint several "incidents" (including randomly firing his rifle into the jungle during sentry duty in the Philippines) ensured he was kept doing menial labour. Weirdly, from the age of 15 he had also been an ardent and open Marxist. In 1959 he emigrated to the Soviet Union, where he applied for citizenship. At first the Russians though they had a publicity coup, but quickly realized that Oswald was too flakey to be of use to them. He was sent to live in Minsk, working as a metal lathe operator, and by January 1961 was reconsidering his defection. From his diary: "The work is drab, the money I get has nowhere to be spent. No nightclubs or bowling alleys, no places of recreation except the trade union dances. I have had enough." Shortly after this he met and married a young Russian woman and they returned with their daughter to the United States in June 1962.
Oswald's actions over the next year and a half were increasingly irrational and erratic, including an attempt to assassinate the anti-communist General Edwin Walker (his role in it was not discovered until after the Kennedy assassination), an attempt to travel to Cuba, and an arrest for passing out pro-Castro handbills.
In November Kennedy was scheduled to visit Dallas, where Oswald worked filling book orders at the Texas School Book Depository. On Friday November 22 he left his wedding ring and $170 at home and came into work carrying a long paper bag. He was last seen by a co-worker alone on the sixth floor of the Depository half an hour before the assassination.
After the shooting he hid the rifle behind some boxes and left the building. After boarding several buses and a taxi, he was stopped by an police officer, whom he shot and killed with a revolver in front of two eyewitnesses. He was eventually arrested trying to blend in with the audience in the Texas Theater; he put up a struggle and tried to shoot but the hammer of his revolver came down on the web of skin between the thumb and forefinger of an officer's hand.
He was arraigned for both the murder of the President and of the police officer. Two days later, while being transferred to Dallas County Jail, Jack Ruby, a Dallas nightclub owner upset by Kennedy's assassination, apprached Oswald and shot him in the belly. You can view Oswald's assassination here. Oswald died in hospital, just 48 hours after the death of the President.