Ganzack

Ganzack was a powerful pirate, seen in the One Piece OVA, with crab-like armor and hidden weapons, who took over the island Medeka resided on and captured some of the people there to forcibly build his base and his pirate ship as well as a missile-like weapon. His plans go awry when Luffy, Zoro, and Nami land on the island. While he manages to capture the three (with Nami faking joining Ganzack's side), they break free and confront Ganzack as he tries to escape on his newly-finished ship. After a bit of fighting with Luffy, Ganzack strikes Medeka during one of his swings and slices her armor's helmet off. Seeing this and believing her dead not to mention Ganzack gloating about it, Luffy goes into a rage and turns the tables. Finally beating Ganzack by punching him into the air just in time for the missile weapon Ganzack launched earlier to come down on the villain, finishing him once and for all.

Trivia

 * The Ganzack Pirates were not a real part of the One Piece series, but they were included in a Japanese movie festival called Jump-Fest 98, in which Defeat the Pirate Ganzack! premiered.
 * His name seems to be a pun of zangyaku (残虐), being a corrupt anagram of the word.