When most people think of "The Beatles" they think of the Fab Four: John, Paul, George, and Ringo. Of this group John Lennon was the first to die followed recently by George Harrison.
There were also some additional members of the original Beatles: Stu Sutcliffe and Pete Best. If these two are considered then Stu would have been the very first one to die.
https://www.biography.com/musician/john-lennon
