Pete Townshend was the guitarist and primary songwriter for the Who from 1964 to 1982, also participating in the group's occasional reunions after its formal breakup. Best-known for his conceptual works, he wrote Tommy and Quadrophenia for the band, as well as the bulk of its other material. He made his first, tentative solo album, Who Came First, in 1972.
It was Pete that Linda told the "I'm gonna marry a Beatle" story to. It's only natural that he and Paul should record together. They're also friends, and Pete was at the Concert for NYC.