Crocodile (One Piece)

Sir Crocodile (サー・クロコダイル, Sā Kurokodairu) is one of the major and longest-running antagonists in the anime and manga, One Piece. He was the president of a secret crime organization called Baroque Works and was a member of the Seven Warlords of the Sea (called the "Shichibukai" (七武海, Seven Military Seas) in the Japanese versions). After he was defeated by the series protagonist, Monkey D. Luffy, he was arrested and sentenced to life imprisonment in Impel Down, a maximum security prison known for being inescapable. He recently was able to escape, however, with the help of Luffy and several other prisoners from Impel Down.

Motives
When he was first introduced, Crocodile was planning to use Baroque Works to stage a faux rebellion and conquer the desert kingdom of Alabasta. His true motive for doing this was to gain access to the poneglyph, special hieroglyphs, that lead to the location of Pluton, a powerful battleship said to have enough power to conquer the world. However, he was betrayed by his former partner, Nico Robin, and was defeated by Luffy. As a result of his true identity being revealed, the World Government striped him of his title and sent him to Impel Down.

Later on, when Luffy broke into Impel Down to rescue his brother, Protgas D. Ace, he ran into Crocodile, and while he was still angry at him for what he had done, Luffy let him go so that he could help him escape from Impel Down, though Crocodile only agreed to do this so that he could have a chance at killing Whitebeard, the strongest pirate in the world.

Powers
Crocodile at the Sand Sand Fruit (Suna Suna no Mi), and is able to turn his body into sand. Not only that, he can also manipulate sand around him, as well as extract the moisture from people and objects, turning them into sand. Like other eaters of the Devil Fruit, he cannot swim and loses his powers when immersed in water or touched by seastone, but another unique weakness is that he loses his ability to turn into sand when he is soaked in water or is touched by something soaked in water. The same also applies to other fluids (i.e., Luffy was able to fight Crocodile using his own blood).