Who's Your Favorite Character Who Went To Insane Lengths For Revenge?

Some great science fiction and fantasy characters are motivated by love, or greed, or a thirst for justice... but a lot of the most unforgettable characters are motivated by a desire for vengeance. What's your favorite story about a character who paid a high price to punish those who had wronged him or her?

Please include a YouTube clip (if possible) showing the best vengeance-seeking character. And please mention his or her name, where he or she appears, and why this quest for retribution had a steep cost.

Top image: His name is Inigo Montoya. Someone killed his father, and that person should prepare to die. (From The Princess Bride, natch.) Artwork by Rabbittooth.