If I were to choose some musician that I believe transcend ordinary and wander into legendary status, here is who I would choose:
1. Moondog
Blinded as a youth, this German musician/composer spent his entire life writing music and learning various instruments. He has so many recordings of his works that it's nearly impossible to pin down one thing of his to listen to, but his 1969 self titled album is incredible, cover to cover.
2. Buckethead
Nobody makes the guitar sound like Buckethead does. Another musician that has really made his instrument an extended part of himself. There are literally hundreds of hours of his work and some of it is just insane.
3. Gregory Porter
Ex-football player Gregory Porter writes his own music, which is incredible when you consider how natural his jazz feels. The man has a voice that is smooth as silk and his words can be extremely moving as well. Jazz has been transformed by him, and he'll be a giant of the genre for decades to come.
4. Gustav Holst
Easily the greatest composer of the early 20th century, Gustav Holst is most known for writing the Planets Suite, which is a monumental piece of music. His string writing is some of the best of the classical genre.
5. Danger Mouse
Writer/Producer Danger Mouse has worked in more genres of music than most people even realize. Everything he touches has this polished feeling of great sound. He understands mixing and layered music that no other producer out there does.
I know I'll think of more, but these are the immediate stand-outs to me.