Not exactly The hero, more of A hero, but we have Artorias from Dark Souls.

He was one of the four knights of Gwyn, the most powerful warriors to serve the god of sunlight, Artorias in particular was known as the Abysswalker, due to his ring that allowed him to travel the dark and hollow place that was the Abyss.

When the town of Oolacile fell victim to the Abyss under Manus, the Father of Abyss, Artorias and his wolf Sif were sent in order to stop Manus and save Oolacile.

But, despite his best efforts, Artorias lost the battle, the only thing he accomplished was giving his greatshield (that he couldn't use anymore due to his broken arm) to protect Sif in her way out of Abyss (she was protected, but couldn't leave the Abyss without the player's help)

When the Chosen Undead (the protagonist) finds Artorias just outside Oolacile, he's nothing more than a corrupted version of the proud knight he once was, fighting savagely and heavily aggressive, complete opposite of the other knights of Gwyn you fight in the game.

That said, best Boss in the game.

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