Step 1 : Introduction to the question "Which 1970s TV sitcom had its theme song reach #1 on the Billboard Hot 100 chart?"
In 1975, John Sebastian, former member of the beloved 60s pop group the Lovin’ Spoonful, was asked to write and record the theme song for a brand-new television show with the working title Kotter. Sebastian had trouble finding rhymes for the word “Kotter” and ended up going with the more general “welcome back” theme. That song, “Welcome Back,” became the #1 song on the charts on this day in 1976. It also led producers to change the show’s title to Welcome Back, Kotter. Sebastian performed the song on the first season of Saturday Night Live, and memorably flubbed the opening lyrics.