Mustafa al Bacterius is a microorganism that controlled Muriel's nervous system and mind in a attempt to sabotage their mission. He is later expelled from Muriel and he infects Eustace by the end of the episode. His first and only appearance was in Mission to the Sun. In the Japanese dub, his seiyuu is Chie Matsuura.
Mustafa is a worm-like creature with a deranged looking face and skinny arms. He wears black gloves, a round helmet, and a jet-pack like belt.
- "My name is Mustafa al Bacterius. I am inside the brain of Muriel. I have come a great distance to sabotage your mission. You humans are not satisfied with messing with your own planet, you feel the need to mess with space also. Well, if the sun wants to fizzle, let it. We like it dark. So, get a flashlight and some D cells, cause it's lights out, space clowns!"
- "I have not yet begun to fight!" (A reference to John Paul Jones.)