Crocodile

Crocodile's outfit during the Impel Down and  Battle of Marineford

Sir Crocodile is the former president of the secret criminal organization, Baroque Works, and the central antagonist of the Baroque Works Saga. He is one of the longest running primary villains of the series, as well as the first enemy to hand Luffy a complete and utter defeat. He is originally introduced as a Shichibukai, but later was stripped of his title after attempting to take control of the desert kingdom, Alabasta. 

He is also known as Mr. 0 as his epithet having a former bounty of 81,000,000.