Mudder may refer to:
- A participant in:
- Mud bogging, a form of off-road motorsport
- Multi-user dungeon, an online game
- Obstacle course racing, a sport in which competitors on foot must overcome obstacles including mud
- Tough Mudder, an endurance event series
- A racehorse that performs well on muddy or wet tracks
- A character in "Jaynestown", an episode of the science fiction television series Firefly
- Mother (pronunciation spelling)
- Marian Mudder, Dutch actor and author