Mr. Mojo Risin is a name that singer of the Doors, Jim Morrison, made up and added to the song L.A woman.

if you unscramble "Mr. Mojo Risin", you'll get "Jim Morrison"

You also don't have to think that long to find out that he was actually referring to his own cock.
but this is okay, because it's Jim Morrison.
and Jim Morrison's cock was one of the eight wonders of the world.

When you eat dirt for the first time and leave your family to build a shack in the woods

Anagram/pseudonym of Doors' lead singer Jim Morrison. He used it as a refrain in the song L.A. Woman.

Jim Morrison himself

Mr. mojo risin is the singer of the doors. The best singer alive. If you do not know the lead singer of the doors is.. un scrambel MR MOJO RISIN.... it spells The singers name... I'll give a hint.... J*m MO**i*ON

MR MOJO RISIN
jim morrison

This fact was proven by John densmore's book. Riders On The Storm.