The Story of Hecarim
Hecarim was once a commander in the armies of the Blessed Isles — a conqueror of legendary ambition who was as brutal in peace as in war. When the Shadow of War arrived on the Isles, most inhabitants were simply consumed. Hecarim chose differently: he ran toward the darkness, and the darkness took him in the way it takes those who choose it, which is to say completely and permanently.
What Hecarim became was a spectral fusion of the man and his warhorse — a centaur-like entity of shadow and cavalry charge, stripped of everything human except the ambition. That survived intact, transmuted into something without purpose, since conquest requires something to conquer and the Shadow Isles offer only more shadow. He leads the Spectral Riders because commanding is what he knows. There is nowhere left to conquer. He does it anyway.
The tragedy of Hecarim — if spectral horrors can have tragedies — is that he chose this. He wasn't surprised or overwhelmed. He saw the darkness coming and rode toward it, because power was always what he wanted and power was what the Shadow Isles offered. The fact that the power is meaningless now, that there is no victory condition in his current existence, is a consequence he didn't calculate. He doesn't have the capacity for regret anymore. That's probably for the best.