Pestilence
The Missing Rider
Pestilence is the oldest of the current Horsemen and a close companion of Death, though the two are rarely seen together. They forfeit the Legion tournament but remain curious about something sleeping beneath the Phlegethon. In return for the Hero’s promise of a real adventure, Pestilence agrees to hear Lachesis and later answers her call to help Conquest. They intend to remember the promised journey.
Sources
AQW Wiki: Pestilence · AQW Wiki: Horseman Of Conquest · Pestilence in the arena · The missing rider’s dialogue