The Spirit of Jazz
In the series 1 episode "Electro" is the first appearance of Howlin' Jimmy Jefferson. His ghost is featured in this episode and referred to as the Spirit of Jazz. In this form he looks the same as he did when he was alive but now has a number of supernatural powers and uses them to possess people such as Howard. Howard apparently made a deal with him years ago in which he would make Howard one of the greatest jazz musicians of all time. From that moment on whenever Howard played an instrument the Spirit of Jazz would possess him and make him do "strange things" such as playing the trumpet so vigorously that his clothes tore off. The story is never fully resolved, however, subsequent episodes have shown Howard playing several instruments without any implication that he is possessed by the Spirit of Jazz. Howard later obtains the voodoo scat record that Howlin' Jimmy made and Vince eats a piece of it which causes one of Howlin' Jimmy's blood cells (referred to as the jazz cell) to try and take over Vince's body. Howard along with Lester Corncrake shrink down and enters Vince's body in an attempt to defeat the jazz cell but end up bringing it out of Vince's body with them and making it much larger. It is eventually defeated by an infected safety pin and walks away complaining, falling over just outside the door of the Nabootique. In the form of the jazz cell, Howlin' Jimmy looks like a ball of black dreadlocks with a head and top hat.
The Spirit of Jazz/Howlin' Jimmy Jefferson is portrayed by Noel Fielding. He appears in three separate forms over the course of the series. It is revealed in the series 3 episode, Journey to the Centre of Punk, that he was a famous jazz musician that lived by the swamps of Mississippi. When he was alive he had black and white skin, red eyes and wore a white suit and top hat. When he discovered he was dying of a "strange swamp fever" he decided to make one final record called Voodoo Scat and mixed it with a drop of his own blood.