Anibal Ascertes is part of the Hellpack, a group of Hellfire Wyverns and Horses that live slightly separated from the rest of the flock. Having started with a few mated pairs made of one of each breed, they take in new wild-born Hellfires and Horses every generation, as mates for their Hellhorse offspring.
Anibal, mate of Agrippa, is one of the founders of the Hellpack. He'd become interested in reading through the records of the flock's lineages, and in how a particular dragon's ancestors could be tracked back for centuries.
He gathered up a small group of Hellfires and Horses and convinced them to come with him and start a "special lineage", something that would be pretty and make their offspring desirable.
The group set up home in the jungle-covered foothills of a mountain range, in a nice conveniently empty (with a little persuasion) fort, which they still inhabit to this day.
The rest of the flock doesn't mind. The Hellpack are a nice guard for that stretch of their territory.