Tetra is the leader of the pirate crew in The Legend of Zelda: The Wind Waker. While she isn't a pure heroine, she's generally good hearted.
You first meet her on your island, and eventually issues between Link and Tetra get a little tense. But they manage to find a common goal.
She even goes down to super-underwater land, and meets the old King of Hyrule.
I wasn't really shocked to learn that she was "Princess Zelda" which is a name given by her birth-right.
I really liked her help when fighting Ganondorf in the final battle. Shooting light arrows while sword-fighting? That's good teamwork.
I was bit dissapointed to see her revert back to her Tetra persona. She returns in Phantom Hourglass, but since I hated that game (thanks to the ever returning timed repeat dungeon) I never made it far enough to finish their story.