Dr. Samuel "Sam" Beckett is a fictional character and the protagonist on the science fiction drama Quantum Leap, played by Scott Bakula.

Initially, the audience knows very little about Samuel Beckett, much as Samuel Beckett knows little about himself due to holes in his memory dubbed the "Swiss Cheese Effect". Over the five seasons, the following details are revealed:

Sam Beckett was born August 8, 1953 in Elk Ridge, Indiana to dairy farmer Jonathan Beckett and his wife Thelma. Sam was a child prodigy, learning to read at age 2 and do calculus in his head at age 5. By the time he was 10, he could beat a computer at chess. He also played piano in a concert at Carnegie Hall. In his teen years, Sam's family was dealt a hard blow when his elder brother, Tom, was killed in Vietnam.

Sam graduated high school at age 16, and following his brother's advice, attended MIT. While at MIT, Sam and his mentor, Professor LoNigro, developed a string theory on time travel ("Her Charm"; see below). Sam went through four years of MIT in two years, and continued through various colleges to eventually obtain seven doctoral degrees in Music, Medicine, Physics, Archeology, Ancient Languages, Chemistry, and Astronomy. During his college years, Sam's father suffered a fatal heart attack; the guilt of his absence during his family's time of need would stay with Sam for years.

As a young adult, Sam was a key member of the Starbright Project (details on the nature of the project were not revealed on the show). It was on the Starbright Project where he would meet some of his closest and most trusted friends: Al Calavicci, a decorated naval officer; a brilliant computer programmer known simply as Gushie; and Dr. Donna Eleese, the love of Sam's life. In the years after the Starbright Project, Sam and Donna were engaged, but Sam was jilted at the altar and never saw Donna again.

On Sam's third leap he meets Donna years before he himself get engaged to her. Realizing that her damaged relationship with her father is the reason why she can never commit to a relationship- as her father left her, she subconsciously feels that any man she meets will inevitably abandon her and thus prevents them from doing so by leaving herself- he drives her out to him so that she might get some closure. We learn later in the episode "The Leap Back" that as a result of this Donna never leaves Sam at the altar and are married to this day.

A few years later, Sam and Al spearheaded Project Quantum Leap, a time travel experiment based on the string theory Sam had developed while at MIT. The PQL facility was located in Stallion's Gate, New Mexico in a primarily underground complex. In 1995, after constructing the necessary machinery, including a holographic imaging chamber and a supercomputer with access to vast historical databases, the project's funds were running thin. Eager to prove his theories, Sam prematurely stepped into the nuclear accelerator chamber and propelled himself back in time.