Scott Bakula was the first actor cast, and thus was asked to read with actors under consideration for the part of Al. Bakula immediately felt a connection with Dean Stockwell during his audition, and lobbied the producers to cast him as Al.
According to Dean Stockwell, his friend Dennis Hopper advised him not to take a role on television so soon after being nominated for an Academy Award (Best Supporting Actor for Married to the Mob (1988)). Stockwell took the role anyway and was nominated for four Emmys and four Golden Globes (and won one in 1990) for his role as Al.
There were several ideas for episodes which ultimately were never used. One had Sam leaping in as Robert F. Kennedy. Another idea would involve an animated episode. The producers even toyed with the idea of leaping Sam in as a baby (this was to be the story of the 14th issue of the Quantum Leap comic book, but production ended after issue 13). Also, Donald P. Bellisario wanted to do an episode where Sam leaps in as Thomas Magnum (from Magnum, P.I. (1980)). It is unclear why that episode never materialized, although in an earlier episode, a character is seen watching "Magnum, P.I.", thus establishing that show as fiction within the Quantum Leap "universe".
In an interview conducted shortly after the series ended, Scott Bakula was asked if there were any particular historical figures or events he would have liked to see Sam involved with. Bakula said he would have liked to have done something with the Kennedys unrelated to the assassination or relationship with Marilyn Monroe.
Sam leaped into every year from 1953 through 1987 at least once, except the years 1977, 1984, and 1986. Sam has leaped into the years 1862 and 1945, the only times that he has leaped out of his lifetime.
Scott Bakula did his own singing in episodes in which Sam leaped into musical performers, or was otherwise called upon to do. Prior to his work on Television, Scott Bakula had done extensive work in Musical Theatre.
Bruce McGill is the only other actor besides Scott Bakula and Dean Stockwell to appear in both the first and last episodes. In the pilot, "Genesis", McGill plays "Weird Ernie" the Air Force engineer. And in the last episode, "Mirror Image", he plays "Al the Bartender".
Almost immediately after the series was canceled, producers announced plans to continue with a series of TV (or perhaps theatrical) movies. Scott Bakula expressed optimism in the projects and stated that he and Dean Stockwell wanted to continue in their roles. Nothing came of the plans, the closest being an announced movie for the Sci FI Channel in the early 2000's which was never produced.
Though no special mention is made during the series, with the exception of Gooshie, Project Quantum Leap is run almost entirely by women. They include: Dr. Donna Eleese, Sam's wife, also a physicist; Dr. Beeks, a medical technician; Teena Martinez, Al's girlfriend and assistant programmer; an unnamed military envoy; and, though she is never seen, Dr. Sammy Jo Fuller, Sam's daughter sired during a leap, also a physicist. In addition, Ziggy, the sentient computer that controls the project, displays female characteristics.
The series actually traces its roots to the original Battlestar Galactica, which Donald P. Bellisario wrote and produced for. The show's revival spin-off, Galactica 1980 was to originally center around Time Travel and returning changes in history back to normal. The concept was dropped after the pilot, but Bellisario stuck with the concept to develop into Quantum Leap. The concept of Sam inhabiting the identity of another person to incorporate change for the better was partly inspired by the 1978 movie Heaven Can Wait, which in itself was practically a "word for word" remake of "Here Comes Mr. Jordan"(1941), with the one exception of changing the lead character from a prize fighter, in "Here Comes Mr. Jordan", to a L A Rams quarterback in"Heaven Can Wait".
Scott Bakula would subsequently star on Star Trek:Enterprise. A number of actors who appeared on Quantum Leap also made appearances on various Star Trek TV series. Most notably, Terry Farrell who co-starred on Star Trek Deep Space Nine, and Robert Duncan McNeill who co-starred on Star Trek Voyager each made guest appearances on Quantum Leap.
In the first few episodes of the series, Al exited the Imaging Chamber by an unseen door which opened like a regular door with a turning knob. By the middle of the first season, the effect was changed to the standard rising door with the blue light shining beyond it.
In the first season, the prologues explaining what Quantum Leap was about were done by Scott Bakula as Sam Beckett. By the time season two began, the narrations were done by Deborah Pratt as the voice of Ziggy.
In the episode "Catch a Falling Star - May 21, 1979" Ernie Sabella plays Manny who in "Man of La Mancha" plays Sancho Panza. Many years later Sabella played the role of Sancho in the Broadway revival of the show.
Throughout the series, Sam often encounter implied younger versions of various celebrities and other figures (Buddy Holly, Woody Allen, Michael Jackson, Stephen King, Sylvester Stallone, Bill Clinton and others). Writers had proposed scenes for others, but the show was unable to get proper authorization from the people or their estates to depict them.
The trivia items below may give away important plot points.
Donald P. Bellisario and Scott Bakula have both expressed their ire with the NBC network over the series finale. Originally Bellisario was asked to write an episode that could function either as a season finale cliffhanger, or as an end to the show. When Bellisario complied, the cast and crew were assured of the series renewal. In the eleventh hour NBC decided to cancel the show after all, and re-edited the ending with title cards revealing the fate of Sam and Al. This was one of at least four endings, at least two of which were filmed. If the show was to end, Bellisario originally planned to have Al and Beth as an old married couple discussing how they would locate Sam who had leaped again. Had the show continued, Bellisario planned to have Sam leap into a space station in the distant future, and Al becoming a leaper himself to rescue Sam.