“One” is a song by Harry Nilsson, famous for its opening line, “One is the loneliest number that you’ll ever do.” The song appeared on Aerial Ballet, Nilsson’s third album.
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.
In 1968, Al Kooper released the song on his debut album I Stand Alone.
In 1969, rock band Three Dog Night covered the song on their debut album. The song was released as a single and became a hit.
The song was also included in the soundtrack of House M.D.