The Beatles’ Sgt. Pepper’s Lonely Hearts Club Band is often called the single greatest album of all time. From the start, it was a revolutionary and influential work, almost changing the pop and rock music landscapes overnight. It was a critical hit as well as a popular one, rocketing to the top of the charts all over the world when it was released at the start of June 1967.

Still, for all of the amazing and innovative music found inside Sgt. Pepper’s Lonely Hearts Club Band, its outside is just as significant. The album's iconic and often imitated cover image has been as much an integral part of pop culture as "With a Little Help From My Friends," "Lucy in the Sky With Diamonds" and "A Day in the Life." More than 50 characters populate the colorful cover -- from recognizable ones (like the Beatles themselves in two different guises) to a bunch of old black-and-white images of faces that appear from another time altogether.

The intricate collage of movie stars, artists, writers and deep thinkers certainly is an intriguing one. But it also begs the question, “Who are all these people?” We’ve combed through each and every face on that cover to give you the answers. After clicking through the Beatles' Sgt. Pepper's Cover Art: A Guide to Who's Who -- which you can do in the above gallery -- you'll never again be left wondering who that one guy is standing next to that old-timey dude behind Paul's right shoulder.