Elvis didn't do much. Just

1) Introduced blues, rockabilly and gospel to their first mass audience.

2)Set the standard for guitar as THE pre-eminent rocknroll instrument.

3)Made an icon of his own voice, one that has been emulated by everyone from Paul McCartney to Phil Ochs.

It is easy to view him in terms of the self-parody he became in the Vegas years. See the 1968 Elvis Live Television special(the famous "comeback" show) to get an idea of the raw talent he possessed as a singer and guitarist.