"Best Friend" is the theme song Harry Nilsson wrote and recorded for the television series "The Courtship of Eddie's Father."

 

The Courtship of Eddie's Father

 

The song has been used in scenes in a number of TV shows such as "The Nanny" and was parodied in "South Park."

 

In 2002, the song was used in a public-service ad called "Big Daddy." And, in 2005, "Best Friend" was used in a commercial for the HBO TV Series "The Sopranos."