The opening chords surprise you: they sound contemporary. Bill Haley, bless him, sounds like something out of the 1940's. Even Chuck Berry, the godfather of rock guitarists, has an early sound. Bo Diddley, though -- there's no mistaking -- that's rock. He must have been the first to distort his guitar.
His most famous song, "Bo Diddley," is an improbable hit; it has no bridge, no chord changes. The infectious beat drives the song from start to finish. Bo Diddley is the only rock artist I can think of who has a beat named after him.
That his big hit was named after himself and he had two albums named Bo Diddley -- not to mention Bo Diddley Is a Lover, Bo Diddley Is a Gunslinger, Bo Diddley's a Twister, Bo Diddley's Beach Party, Go Bo Diddley and many more -- prove him to be a master of self-promotion. Leftists might write something cynical here or excuse his blatant self-interest as what a black man had to do to succeed in a white man's world. Altruists always assume there must be something wrong with self-interest and the pursuit of profit; this keeps them at odds with capitalism -- and human nature. I prefer to think he was just cheerfully proud of who he was and he marketed the hell out of it. Bo Diddley became a brand name. That's show biz.
He was an American original.
(Billy Beck met him once.)
UPDATE: Slight revision.