"One" is a song written by Harry Nilsson and made famous by Three Dog Night whose cover in 1969 reached number five on the U.S. Billboard Hot 100 and number four in Canada. The song is known for its opening line "One is the loneliest number that you'll ever do". Nilsson wrote the song after calling someone and getting a busy signal. He stayed on the line listening to the "beep, beep, beep, beep..." tone, writing the song. The busy signal became the opening notes of the song.
The song was sung by Nathan Lane and was featured on the soundtrack Stuart Little 2 in 2002.
In 2004, the song appears in the third episode of House ("Occam's Razor"). Dr. House references the song's opening line during a discussion with his team, and the song later plays over the episode's last scene.
Also in 2004, the song is briefly sung by Donkey in the film Shrek 2.
The Muppets and Jimmy Fallon performed an impromptu rendition of the song on the set of Late Night with Jimmy Fallon while rehearsing for the 2009 Christmas performance.