[Endoperez]

The plague carrier icon was only added few patches back, so it's no wonder you haven't seen it.

Orion the Eternal Knight leads a mercenary band. They are a group of 5 or so human-sized beings wielding flaming swords. Their backstory says they were imprisoned somewhere for a long time, so they have huge starting ages and start with huge amount of experience. How did you "raise" him? It sounds as if you used Ritual of Rebirth to create a mummy out of him. The mummy doesn't necessarily have high-enough maxage to keep ancient beings from getting old age penalties, and has plague carrier ability IIRC.