Monkey D luffy. He may not be the most powerful character in One Piece, but he will become the pirate King by sheer willpower and charisma.
Roronoa Zolo: Luffy's right hand man and First Mate of the Going Sunny, the pirate ship of the Strawhats. Zolo is a damage sponge, no matter how injured he gets (and he is easily the most injured Strawhat) he gets up and keeps on fighting to protect his team and innocents from the navy and other pirates.
Son Goku. He is one of the most persistant characters in Dragonball, overcoming trials many couldn't and becoming stronger and surviving battles by sheer will. He became the most powerful character in the series, but at the beginning he had many enemies stronger than him.
I now present to you my regular guest: Mr. Norman Osborn!
Thank you Geordie Green Lantern. Today I approve of: willpower.