Mad Jack is the 3rd world boss of the videogame Donkey Kong 64. He is encountered at the end of the Frantic Factory level where he serves as the first boss to be fought by Tiny Kong.
Mad Jack has a brownish-green left eye and a red robotic right eye and wears what seems to be a red smock, which is scratched at the front and side. He also wears orange gloves with holes in them. Mad Jack has a green head with seven spikes made entirly out of metal. Through the holes in the gloves, coils can be spotted. This suggests that his fingers are made out of springs, as well as his arms. His box is orange with different objects like a spiral, sparkles and a question mark on it, as well as a blue rim on the edge.
- Mad Jacks voice sounds distinctly similar to Donald Ducks.
- Mad Jack seems to be the only boss in the game that is not allied with King K. Rool.
- The trap door he's dropped through reads REJECT, this combined with his decrepit appearance provides the assumption that Mad Jack is extremely defective.