Quantum Leap was an American television series that was broadcast on NBC from March 26, 1989 to May 5, 1993, for a total of five seasons. The series was created by Donald Bellisario, and starred Scott Bakula as Dr. Sam Beckett, a physicist from the (then future) year of 1997, who becomes lost in time following a time travel experiment, temporarily taking the places of other people to "put right what once went wrong". Dean Stockwell co-starred as Al Calavicci, Sam's womanizing, cigar-smoking sidekick and best friend, who appeared as a hologram that only Sam, animals, and young children could see and hear.
The series featured a mix of comedy, drama and melodrama, social commentary, nostalgia and science fiction, which won it a broad range of fans. One of its trademarks is that at the end of each episode, Sam "leaps" into the setting for the next episode, usually uttering a dismayed "Oh, boy!" Despite struggling on Friday nights at 9 PM in its brief first season, NBC surprisingly renewed the series because of its impressive 18-49 demographics. The series was moved to Wednesdays at 10 PM where it flourished against other fan-favorite series, Wiseguy and China Beach. It was moved twice away from Wednesdays (to Fridays at 8 PM in the fall of 1990 and to Tuesdays at 8 PM in the fall of 1992) where it floundered. The series finale aired in its successful Wednesday 10 PM slot in May 1993. in 2004 and 2007, Quantum Leap was ranked #15 and #19 on TV Guide's "Top Cult Shows Ever".
Throughout the series, Sam believes that God, or some other higher power, is controlling his leaps, sending him to times and places where he may be needed. In the series' final episode, he encounters a mysterious bartender who insinuates detailed knowledge of Sam's "mission" and his true identity. Because this bartender (or someone who looks exactly like him – both parts played by Bruce McGill) was also present in Sam's first leap (although there is no mention of this in the actual episode), Sam comes to believe he might actually be that higher power, though the man neither confirms nor explicitly denies this.
The bartender helps Sam remember that he built Project Quantum Leap exactly because he wanted to put right what once went wrong and makes him realize that he himself has control over his leaps. The bartender then asks Sam where he wishes to leap to next. Sam replies by saying he wishes to return home but he cannot as he still has a wrong to put right for Al, by letting his first wife Beth (Susan Diol in her second appearance in that role during the series) know that Al is still alive in a POW camp in Vietnam (when Sam first encountered Al's wife in the season 2 finale "M.I.A." he refused to tell her, because he felt it was wrong since that wasn't what he was there to change). Sam then promptly leaps out and does so as himself, not in a host body from the past. The show's epilogue states that Sam never returned home, however Beth and Al are still married and they have four daughters.
The show's premise and the pattern of each episode is established in the first episode. Sam appears in the past with no memory of who he is or how he got there. Referred to frequently throughout the series as a "swiss-cheesed brain", 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. Admiral Al Calavicci (Dean Stockwell), a naval officer and Sam's best friend, appears to him as a hologram and explains that Sam is the victim of a time travel experiment that went "a little kaka." Now Sam is lost in time, and his colleagues are unable to bring him back to his own time. Series creator Donald Bellisario once said in an interview that he got the idea for the series from movies like Heaven Can Wait (1978), a remake of the 1941 film Here Comes Mr. Jordan. Bellisario felt the premise, if handled correctly and put in a science fiction setting, could work.
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. Al explains that their best theory to what's going on is that "God, time, fate, or whatever" wants Sam to save the man before he can "leap out." Sam does so, but instead of returning to his own time he leaps into yet another person's life and once again tries 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), he tries to right some wrong or misfortune in the life of that person or someone close to them.