Springsteen and Rourke
Bruce Springsteen and Mickey Rourke met at the Stone Pony back in the eighties. They became motorcycle cruising buddies in 1989 and 1990 when Springsteen was living in Los Angeles, CA. Rourke owned a short-lived club in Los Angeles called Rubber Club, and Springsteen is known to have made two onstage appearances in that club.
According to Aronofsky, Springsteen is a huge fan of Rourke's. He's seen every movie of his and he was hoping for him to get back on track making movies. He was following him and he wanted to know about his projects. Bruce heard about the movie so he called Mickey and asked him how he was doing. Mickey gave him the script; Bruce read it and said he loved it, nothing more.
Composition
Springsteen wrote THE WRESTLER in Europe during the Magic Tour, sometime between late May and early July 2008. In July, he called Rourke and Aronofsky complimenting them on the movie and adding that he wrote a song for the film's character. The song came while the movie was at the end of its editing phase. This late addition caused the movie's screening debut to take place at the end of the Venice Film Festival.
The Song
On THE WRESTLER, Springsteen handles guitar, piano, and vocals. Director Darren Aronofsky described it as "a wonderful acoustic piece; makes me choke up every time I hear it. [Springsteen] really captured the spirit of the film and Mickey [Rourke]'s character in the piece."