Who's on First? is a vaudeville comedy routine made most famous by Abbott and Costello. In Abbott and Costello's version, the premise of the routine is that Abbott is identifying the players on a baseball team to Costello, but their names and nicknames can be interpreted as non-responsive answers to Costello's questions. In this context, the first baseman is named "Who"; thus, the utterance "Who's on first" is ambiguous between the question ("which person is the first baseman?") and the answer ("The name of the first baseman is 'Who'").

"Who's on First?" is descended from turn-of-the-century burlesque sketches that used plays on words and names. Examples are "The Baker Scene" (the shop is located on Watt Street) and "Who Dyed" (the owner is named Who). In the 1930 movie Cracked Nuts, comedians Bert Wheeler and Robert Woolsey examine a map of a mythical kingdom with dialogue like this: "What is next to Which." "What is the name of the town next to Which?" "Yes." In English variety halls (Britain's equivalent of vaudeville theatres), comedian Will Hay performed a routine in the early 1930s (and possibly earlier) as a schoolmaster interviewing a schoolboy named Howe who came from Ware but now lives in Wye. By the early 1930s, a "Baseball Routine" had become a standard bit for burlesque comics across the United States. Abbott's wife recalled Bud performing the routine with another comedian before teaming with Costello.

James Thomas "Jimmy" Fallon, Jr. (born September 19, 1974) is an American actor, comedian, singer, musician and television host. He currently hosts Late Night with Jimmy Fallon, a late-night talk show that airs Monday through Friday on NBC. Prior to that he appeared in several films, and was best known as a cast member on Saturday Night Live from 1998–2004.

James Thomas Fallon, Jr., was born in Brooklyn, New York. Jimmy is the son of Gloria and James Fallon, Sr., who is a Vietnam War veteran. His family later settled in Saugerties, New York, while his father worked at IBM in nearby Kingston, New York. He is of Irish descent. As a child, he and his older sister, Gloria, would reenact the “clean parts” of Saturday Night Live that his parents had taped for him. Fallon was such a fan of Saturday Night Live that he made a weekly event of watching it in his dormitory during college. In his teens, he impressed his parents with different impersonations, the first being of James Cagney. He was also musically inclined, and started playing guitar at age 13. He would go on to mix comedy and music in contests and shows.

William Edward "Billy" Crystal (born March 14, 1948) is an American actor, writer, producer, comedian, and film director. He gained prominence in the 1970s for playing Jodie Dallas on the ABC sitcom Soap and became a Hollywood film star during the late 1980s and 1990s, appearing in the critical and box office successes When Harry Met Sally... and City Slickers. He has hosted the Academy Awards nine times, including the 84th Academy Awards in 2012.

Crystal was born in the Doctor's Hospital in Manhattan and raised on Long Island in Long Beach, the son of Helen (née Gabler), a housewife, and Jack Crystal, a record company executive and jazz producer who also owned and operated the Commodore Record store. His babysitter was occasionally Billie Holiday. His uncle was musician and songwriter Milt Gabler, and his brother, Richard "Rip" Crystal, is a television producer. Crystal grew up in a Jewish family that he has described as "large" and "loving".

After graduation from Long Beach High School, Crystal attended Marshall University in Huntington, West Virginia on a baseball scholarship, having learned the game from his father, who pitched for St. John's University. Crystal never played a game at Marshall because the program was suspended during his freshman year, and because he was too busy being the Editor in Chief of The BG News from 1969–70. He did not return to Marshall as a sophomore, staying back in New York with his future wife. He instead attended Nassau Community College and later New York University, where he graduated in 1970 with a BFA from its Tisch School of the Arts.

Jerome Allen "Jerry" Seinfeld (born April 29, 1954) is an American stand-up comedian, actor, writer, and television and film producer, best known for playing a semi-fictional version of himself in the sitcom Seinfeld (1989–1998), which he co-created and co-wrote with Larry David, and, in the show's final two seasons, co-executive-produced.

In his first major foray back into the media since the finale of Seinfeld, he co-wrote and co-produced the film Bee Movie, also taking on the lead role of Barry B. Benson. In February 2010, Seinfeld premiered a reality TV series called The Marriage Ref on NBC. Seinfeld directed Colin Quinn in the Broadway show Long Story Short at the Helen Hayes Theater in New York which ran until January 8, 2011.

Seinfeld is known for specializing in observational humor, often focusing on personal relationships and uncomfortable social obligations. Comedy Central ranked Jerry Seinfeld as one of the twelve greatest stand-up comedians of all time in its four-part special The 100 Greatest Standups Of All Time.

Bob Greenberg (born 1954) was one of the earliest employees of Microsoft. Before leaving Microsoft in 1981, he had arranged to have a picture of the original Albuquerque team taken that has since received widespread exposure. He has continued as a consultant in the computer industry. However, the widely disseminated estimate of his wealth and number of houses has been overstated.

Bob went to, and briefly taught at, Harvard University where he first met Bill Gates. He has also worked or consulted for The RAND Corporation, the pre-breakup AT&T, and a number of startup technology ventures. Bob has been involved in system programming, artificial intelligence, golf software, UNIX and XENIX, business consulting, and teaching computer science.

After the 9/11 tragedy happened, Bob changed his primary focus and has since been serving as the president of several Jewish non-profit organizations.