Complex sentence: A tremendous man covered in armor and the leader of the Flying Fish Riders, no one knows Duval's true identity but he apparently has a history with one of the male Straw Hat Pirates (probably Luffy), and wants revenge for some past wrongs.
Split into simpler sentences: A tremendous man covered in armor and the leader of the Flying Fish Riders. No one knows his true identity but he apparently has a history with Luffy, and wants revenge for some past wrongs.