Determinator

Everything About Fiction You Never Wanted to Know.
But even as hope died in Sam, or seemed to die, it was turned to a new strength. Sam's plain hobbit-face grew stern, almost grim, as the will hardened in him, and he felt through all his limbs a thrill, as if he was turning into some creature of stone and steel that neither despair nor weariness nor endless barren miles could subdue.
The Lord of the Rings: Return of the King

A character - good guy or bad, male or female, young or old - who never gives up. Ever. No matter what.

There is no stopping the Determinator. They do not understand tact. They do not Know When to Fold'Em, and it's a waste of time to tell them the odds. No one can reason with them. They'll do whatever they have to without question. No price is too great to pay for success, up to and including their own life (and others'). Do not expect them to realize they might be better off letting it go, even if they can barely stand. If you're ever kidnapped or lost with no hope of rescue, they'll be the one who will find you. Their adversaries will shout, in exasperated rage, "Why Won't You Die?!". For them, there is no line between "perseverance" and "insanity."

The nobility of their goal is not necessarily proportionate to their persistence. This is just as often an obsessive rival with a grudge as it is a hero on a chivalrous quest, and where their willpower ultimately leads them will depend both on their role and on where the work stands on the Sliding Scale of Idealism Versus Cynicism. Heroes- especially Badass Normals with a Screw Destiny attitude- will defeat villains by virtue of being too stubborn to stay down. Anti Heroes will Jump Off The Slippery Slope, forsake The Powers of Love and Friendship, become like that which they fight and walk the thin line between victory and tragedy. Villains will refuse to admit defeat, resist seemingly fatal punishment, hunt their prey tirelessly and let the heroes know that We Will Meet Again.

In the Shonen anime, it's comparatively rare to find a main character who isn't one of these.

Compare Suicidal Overconfidence, a common feature of many Video Game genres where enemies will always, blindly, and relentlessly be at your throat with no regard for how horribly you are massacring them (though this is more due to genre requirements than characterization). Compare and contrast Implacable Man, who suffers no apparent damage at all. Compare Tragic Dream, where becoming a Determinator can only end in tears. Can be identified by their trademark Determined Expression.

See also Heroic Resolve, Heroic Spirit, Lawful Stupid Chaotic Stupid, Plucky Girl, Principles Zealot, The Unfettered, The Fettered, Unconscious Objector, and Stiff Upper Lip.

Examples of Determinator are listed on these subpages: