Jack Harold Paar (May 1, 1918 – January 27, 2004) was an American talk show host, writer, radio and television comedian, and film actor. He was the second host of The Tonight Show from 1957 to 1962. Time magazine's obituary of Paar reported wryly, "His fans would remember him as the fellow who split talk show history into two eras: Before Paar and Below Paar."

Jack Harold Paar was born on May 1, 1918, in Canton, Ohio, the son of Lillian M. (née Hein) and Howard Paar. He moved with his family to Jackson, Michigan, about 40 miles (64 km) south of Lansing. As a child, he developed a stutter, which he learned to manage. He contracted tuberculosis when he was 14 and left school at 16.

After dropping out of Jackson High School, Paar worked as a broadcaster for WIBM, a local radio station. He went on to work as a humorous disc jockey at other Midwest stations, including WJR in Detroit, WIRE in Indianapolis, WGAR in Cleveland, and WBEN in Buffalo. In his book P.S. Jack Paar, he recalled doing utility duty at WGAR in 1938 when Orson Welles broadcast his famous simulated alien invasion, The War of the Worlds, over the CBS network and its WGAR affiliate. Attempting to calm possibly panicked listeners, Paar announced, "The world is not coming to an end. Trust me. When have I ever lied to you?"

In 1943, Paar was drafted into the U.S. Army during World War II, which interrupted his tenure as host of WBEN's morning show The Sun Greeter's Club. He was assigned to the Special Services in the South Pacific to entertain the troops. Paar was a clever, wisecracking master of ceremonies; he narrowly escaped being disciplined when he impersonated senior officers.

After World War II, Paar opted not to return to WBEN, instead seeking opportunities in network radio and film. He worked in radio as a fill-in on The Breakfast Club show and appeared as a host of Take It or Leave It, a show with a top prize of $64.

In 1947, Jack Benny, who was impressed by Paar's U.S.O. performances, suggested that Paar serve as his 1947 summer replacement. Paar was enough of a hit on Benny's show that Benny's sponsor, the American Tobacco Company, decided to keep him on the air, moving him to ABC for the fall season. Paar later refused American Tobacco's suggestion that he come up with a weekly running gag or gimmick, saying he "wanted to get away from that kind of old-hat comedy, the kind being practiced by Jack Benny and Fred Allen." The show was then terminated, earning Paar the enduring image of "a spoiled kid". A profile of Paar by the Museum of Broadcast Communications suggests that Paar later emulated Benny's mannerisms.

Paar signed as a contract player for Howard Hughes' RKO studio in the immediate postwar period, appearing as the emcee in Variety Time (1948), a low-budget compilation of vaudeville sketches. He later recalled that RKO producers had trouble figuring out what kind of screen characters he could play until one of the executives dubbed him, "Kay Kyser [bandleader who had made films for RKO], with warmth." Another compared his leading man appearance with Alan Ladd. Paar projected a pleasant personality on film, and RKO called him back to emcee another filmed vaudeville show, Footlight Varieties (1951). He also appeared in the 1950 film Walk Softly, Stranger, starring Joseph Cotten. In 1951, he played Marilyn Monroe's boyfriend in the 20th Century Fox film Love Nest.

Paar returned to radio in 1950, hosting The $64 Question for one season, then quitting in a wage dispute after the show's sponsor pulled out and NBC insisted everyone involved take a pay cut.