Music as we know it would not be possible without Les Paul. Not only was he an immensely influential guitarist, but he also did extensive early work on the electric guitar. Originally he attached the components to a railroad tie to prove that it could be done. Later he designed the guitar that bore his name and became hugely popular among musicians. Even now people who play electric tend to choose either a Fender or a Gibson Les Paul.
But his biggest contributions may have come in recording technology. Paul invented multi-track recording and close-mic recording, among other innovations.