The Story of Aatrox
Aatrox is the oldest of the Darkin — the god-warriors of Shurima who were corrupted by the weapons they wielded and imprisoned within them after the Targonians decided they had become too dangerous to live. He was the first to fall, which means he has been imprisoned the longest, which means the centuries of his imprisonment accumulated into the specific kind of rage that has no target large enough to satisfy it. He hates everything, in an order of priority that starts with the Targonians who imprisoned him, the Aspects who oversaw it, and everything else that has had the misfortune of existing within reach since.
When a mortal takes up his sword, he consumes them from within — using their body as a vessel while draining their will and eventually their existence. He has had many hosts across the centuries. None of them persisted. He views this as he views most things: inevitable, appropriate, a small expression of a power that was always going to claim what it needed. He does not pretend otherwise. Aatrox is honest about what he is in the way that only something ancient enough to have stopped caring about pretense can be.
He wants to die. This is the secret beneath the rage: the true death, the ending that his imprisonment denied him, the silence that he has been unable to reach because the sword keeps him alive regardless of how thoroughly the body he inhabits is destroyed. He destroys because destruction brings him closer to the ending he seeks. He fights because fighting is the language he was made to speak. He is the World Ender, and what he most wants to end is himself.