Magellan

Magellan is the former warden, now the vice-warden of Impel Down. Due to his actions he is the main villain of the Impel Down Arc. After his failure during the prison escape he attempted to commit suicide which only put him in the hospital. He is known for eating poison lunches which oftenly causes him to have diahrrea for the majorty of the day.

Devil Fruit
Magellan ate the Paramecia-type Venom-Venom Fruit which allows him to be secret poison from his own body. With this, he uses this poison to create a huge monster known as the Hydra. Also, anyone who is coated in his poison will only have 24 hours to live as seen with Luffy (though he surivies later on).

Trivia

 * Magellan is one of few characters in the series not to be fully defeated by Luffy at all in battle. During the first fight, Magellan defeated Luffy. During the second fight, Magellan shifted to his most deadly poison that forced Luffy to retreat.
 * Magellan is the first character to have a devilish appearance with the second being Caesar Clown.