"They say he made a deal with the devil. Standard blues musician rapsheet." - Senator Stampingston on Mashed Potato Johnson

Mashed Potato Johnson (Voiced By Brendon Small) is the oldest living blues guitarist in the world. He is a parody of Robert Johnson, exemplified by their both having supposedly sold their souls to the devil in order to gain blues fame.

He is initially shown in the episode "Bluesklok," in which he teaches Dethklok the blues to rid them of their celebrity depression. At the end of their training, he takes the band to sell their souls to the Blues Devil. After the band fails to complete this task, he tells them to play a show, during which the Blues Devil is seen watching the carnage caused by Dethklok's mastery of the blues.

He later appeared on the Dethalbum bonus disc on the song "Murdertrain A 'Comin" in a speaking role, accompanying Skwisgaar for a smooth blues solo.

He also appeared in "FatherKlok" as one of Skwisgar's potential fathers.