Paul Allen Wood Shaffer CM (born November 28, 1949) is a Canadian musician, actor, and comedian who served as David Letterman's musical director, bandleader, and sidekick on Late Night with David Letterman (1982–1993) and Late Show with David Letterman (1993–2015).

Shaffer was born in 1949 in Toronto, and raised in Fort William (now part of Thunder Bay), Ontario, Canada, the son of Shirley and Bernard Shaffer. He was raised in the Jewish faith. His father, a lawyer, was a jazz aficionado while his mother loved show tunes. When Shaffer was 12, his parents took him on a trip to Las Vegas where they took in Nat King Cole and other shows; this was an experience Shaffer described later as "life changing" and led to his decision to become a performer. As a child, Shaffer took piano lessons, and in his teenage years played the organ in a band called Fabulous Fugitives with his schoolmates in Thunder Bay. Later, he performed with the "Flash Landing Band" at different venues around Edmonton and the interior of British Columbia. Educated at the University of Toronto, he began playing with jazz guitarist Tisziji Muñoz, performing in bands around the bars there, where he found an interest in musicals, and completed his studies, with a Bachelor of Arts degree in sociology in 1971.

Shaffer appears briefly, playing an organ at an outdoor wedding, in North of Superior (1971), an early IMAX documentary shot in northern Ontario.

Shaffer began his music career in 1972 when Stephen Schwartz invited him to be the musical director for the Toronto production of Godspell, starring Victor Garber, Gilda Radner, Martin Short, Eugene Levy, Dave Thomas, and Andrea Martin. He went on to play piano for the Schwartz Broadway show The Magic Show in 1974, then became a member of the house band on NBC's Saturday Night Live (SNL) television program from 1975 to 1980 (except for a brief departure in 1977). Shaffer also regularly appeared in the show's sketches, notably as the pianist for Bill Murray's Nick the Lounge Singer character, and as Don Kirshner. He also appeared as a keyboardist on the 1978 album Desire Wire, recorded by pop/rock star, musician, and backing vocalist Cindy Bullens.

Shaffer occasionally teamed up with the Not Ready for Prime-Time Players off the show, as well, including work on Gilda Radner's highly successful Broadway show and as the musical director for John Belushi and Dan Aykroyd whenever they recorded or performed as the Blues Brothers. Shaffer was to appear in the duo's 1980 film, but as he revealed in October 2009 on CBS Sunday Morning, Belushi dropped him from the project. In a memo to fellow SNL colleagues, Belushi said that he was unhappy that Shaffer was spending so much time on a studio record for Radner. Belushi said that he had tried to talk Shaffer out of working on the album in the first place to avoid sharing Shaffer's talents with another SNL-related project. Shaffer later reported that he was in (unrequited) love with Radner. He went on to appear in 1998's Blues Brothers 2000.

Shaffer left SNL in 1977 for a few months to co-star with Greg Evigan in A Year at the Top, a short-lived CBS sitcom in which Shaffer and Evigan play two musicians from Idaho who relocate to Hollywood, where they are regularly tempted by a famous promoter (who is actually the devil's son), played by Gabriel Dell, to sell their souls in exchange for a year of stardom. Though the series only lasted a few episodes, a soundtrack album was released.

Following the series' cancellation, Shaffer returned to SNL during the show's third season during the 1977-78 season. He was named a cast member during the 1979-80 season as a featured player, making him the first and only band member to join the cast. In the spring of 1980, Shaffer became the first person to say "fuck" on SNL. That year, SNL parodied The Troggs Tapes with a medieval musical sketch featuring Shaffer, Bill Murray, Harry Shearer, and a "special guest appearance" by John Belushi (who had left the show the previous year). In the middle of a long tirade that featured repeated use of the word "flogging", Shaffer inadvertently uttered the forbidden word. It not only escaped the censors in the live broadcast and the West Coast taped airing, but also reappeared in the summer rerun, and even in the syndicated versions of the show for several years.

Shaffer, along with executive producer Lorne Michaels, the entire cast, most of the writing staff, and several other band mates, left the show at the end of the season, after five years. Decades after leaving the show, Shaffer recounted that Jean Doumanian (who was taking over as producer the next season) offered him to be the new musical-director in light of Howard Shore leaving, but he turned it down. Citing in part that he didn't want to start the show again with a brand new cast, and he felt five years was enough time to do the show.