"One" is a song written by Harry Nilsson and made famous by Three Dog Night whose recording reached number five on the U.S. Billboard Hot 100 in 1969 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.
Electric Six recorded a cover version of the song for use in the trailer for Army of Two, but their version was rejected in favour of the Mastodon version. It was subsequently included on their 2015 complilation album Mimicry and Memories.
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.