Theodoric was a grog sergeant at the previous covenant, who survived its destruction and then lived in its (somewhat rebuilt) ruins until the new covenant found him there. After some application of Intellego Mentem magic (which he doesn't actually know about), he was appointed a custos, and has served as a generally useful sorce of local knowledge.
Personality wise, he's cautious but with a tendency to be very loyal to something once he puts his mind to it.
His character sheet is here: https://forum.atlas-games.com/t/covenfolk-character-sheets/5242/1 .