Quantum Leap (1989)

In the series' first episode, Sam appears in the past with no memory of who he is or how he got there. Referred to often throughout the series as the "swiss cheese effect," Sam's partial amnesia prevents him from remembering most of the details of his own life... all he knows is that he's not who everyone in the past seems to think he is. Fortunately Admiral Al Calavicci (Dean Stockwell), Sam's best friend, appears to him in holographic form and explains that Sam is the victim of a time travel experiment that went wrong. Now Sam is lost in time, and his colleagues are having difficulty "retrieving" him and bringing him back to his own time.

Sam soon learns that the man he replaced in the past (or "leaped into," in the show's parlance) is an Air Force test pilot who was about to be killed during a botched flight. Sam saves the man (as well as his wife and unborn child), believing that doing so might enable him to return to his own time, but soon "leaps" again and finds himself living yet another person's life, and once again trying to "put right what once went wrong." In each episode, Sam leaps into a new host, often finding himself in dangerous, embarrassing, or otherwise compromising positions, and with Al's help (and that of his colleagues, who have access to information from the future), tries to right some wrong or misfortune in that person's life.

Sam believes that God, or some other higher power, is controlling his leaps, sending him to times and places where he is needed. In the series' final episode, he even encounters a mysterious man, a bartender who insinuates knowledge of Sam's "mission" and his true identity, whom Sam comes to believe might actually be that higher power (though the man denies this). It should be noted that this mysterious bartender was also in the show's first episode and Sam's first leap, lending credence to Sam's belief that this man is the manifestation of a "higher power" who had observed his first leap in order to see if Sam could put right the past's wrongs.

Several characters are referred to throughout the series, but rarely (if ever) actually appear. Ziggy, the artificial intelligence that runs the project and supplies Al with information to help figure out the purpose of Sam's leaps, only appears in one episode, and Gushie, the project's head programmer (who has chronic halitosis and is reputedly having an affair with Al's long-time girlfriend, Tina) only appears in six episodes, including both the pilot and the finale. Dr. Beeks, the project psychiatrist, is also frequently mentioned, but only appears in two episodes.