Summertime is the most recorded song, with 67,591 recordings as of June 2017. However, some argue that recordings don't equal covers, as a band could cover a hit and create multiple recordings in the studio or live. Most sources rate it in the top ten, but not #1, as that honor goes to The Beatles' hit, Yesterday.
Sir Paul McCartney grew up in a working-class family in Liverpool, UK. His father sold cotton and was a jazz musician, and his mother died when he was 14. His father encouraged him to learn music, and Paul's natural talent led to him writing songs such as When I'm 64 by the time he was 16. He met John Lennon, who invited him to join his band, The Quarrymen.
Paul McCartney dreamed of the song's melody one night in 1964 and began writing lyrics for it, eventually finishing it with the working title "Scrambled Eggs" and the second line "Oh my baby, how I love your legs". He worked on the words while they were shooting Help! and played the tune and sang scrambled eggs so much that the film's director told him to finish it or give up. He woke up one morning and had bits of it in his head, and over the next few weeks, he finished the song. This lengthy writing process was unusual for Paul, who often completed songs in hours, but this labor of love was all McCartney, even though he credited Lennon.