Mozart has to many qualities to not be the answer, honestly.
That said, while quietly flying under the radar, Rik Emmett is probably the very best guitarist AND singer ever. There are people who are better at each craft, but not at both. He's demonstrated remarkable versatility in his playing. He's written fantastic songs. He was a great showman. Right up to the point he packed up and dropped out of a successful band because he wanted to do his own thing making 1/100th of the money.