Written and first recorded by Nilsson (1967).
Also recorded by Al Kooper (1968).
Hit versions by Three Dog Night (US #5/CAN #4 1969), Johnny Farnham (AUS #1 1969).
From the wiki: “‘One’ was written by Harry Nilsson and recorded in 1967. It appeared initially on Nilsson’s third album, Aerial Ballet, released in 1968. 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 was expressed musically to become the opening notes of the song.
“In 1968, Al Kooper released the song on his debut solo album I Stand Alone. In 1969, Three Dog Night covered the song on their debut album Three Dog Night, with Chuck Negron on lead vocal. Their version was released as a single and became a hit, reaching #5 on the Billboard Hot 100. That same year, the song was covered by Australian singer Johnny Farnham, reaching #4 on the Australian charts.”
Al Kooper, “One” (1968):
Three Dog Night, “One” (1969):
Johnny Farnham, “One” (1969):