Magellan

Magellan is the chief warden in charge of Impel Down.

Appearance
Magellan is a large man that greatly resembles a devil. He has bat wings, and a gargoyle-like face. He has horn-like ornaments on his head which he can pull out and use as weapons. Underneath them, he has short black twintail-styled hair. He towers over a regular sized person greatly. He also has very sharp teeth and his hands closely resemble those of the Blue Gorillas.
Personality
Magellan is a man with a rather distinct problem. Because of the powers of the Doku Doku no Mi, he delights in eating poisoned food. Though immune to the poison, he suffers from a severe case of diarrhea brought on from ingesting such poisonous meals. As a result, he spends approximately ten hours each day in the bathroom relieving himself. He is actually agoraphobic and enjoys dark, enclosed spaces.
Though he only performs roughly four hours of duty as Warden of Impel Down due to his insistence to eat poisonous foods, despite the severe diarrhea, he still takes his role of keeping the prisoners in check seriously, and does not tolerate their bad behaviors. As he has permission to execute any one of them he sees fit, he shows no hesitation to drench them in his Hydra's lethal poison. Magellan also takes great pride in keeping Impel Down's reputation of being impenetrable and inescapable, and felt personally insulted when Monkey D. Luffy besmirched that record since Kinjishi the "Flying Pirate" 20 years ago.
Magellan seems to find it amusing whenever someone he doesn't particularly like gets poisoned or suffocated by his powers, evident when he was seen chuckling at Hannyabal after he sighed a poisonous mist at the latter's direction. While he also does not tolerate Hannyabal's "poisonous" (the actual term used is punned with the word "distant") comments he himself is prone to use them against himself. His ruthlessness applies not only to the prisoners, but also to his own men, as seen berating a guard who was accidentally poisoned by his Hydra.
Despite his ruthlessness and seriousness, Magellan was one of the many to fall for Boa Hancock's beauty, and neglected to hear the report of Luffy's intrusion when she requested to see Ace immediately, being completely head-over-heels over her.
Abilities and Powers
As the warden of Impel Down, Magellan has full control of the prison. However because of his constant diarrhea, he spends most of his time in the bathroom. Adding to fact that sleeps approximately eight hours per day and discounting meal times and breaks, he only works for approximately four hours per day doing his job.
Nonetheless, he has both the authority and power to execute any of the prisoners in Impel Down as he sees fit.
Devil Fruit
Magellan had eaten the Doku Doku no Mi, a Devil Fruit that allows him to generate and manipulate poison. Magellan can produce these poison in different strength and forms, such as breathing simple minor gas to put subordinates in place, blowing tear gas bubbles to stun the opponents, or create extremely fatal liquid poison. His most infamous technique that is well known to most prisoners within the walls of Impel Down is a three-headed dragon called the Hydra, which is composed of corrosive liquid poison that causes lethal nerve-paralysis and melts the victims at the same time. His Hydra also had the power to easily defeat the Blackbeard Pirates with little to no effort.
Because of the fruit's powers, Magellan is also able to eat poisoned food without killing himself, where instead it gives the food flavor. However, while he is immune to the poison, the food instead causes him to have diarrhea. This being a problem as he loves to eat poisoned food.

(Source: One Piece Wikia)