I'd say a Beatmaster that can use most of the orb vallis and plain of eidolon animals that you catch as companions for his abilities, maybe something like interchangeable abilities depending on what you went out to capture.
If i were to suggest lore, maybe something about it being forgotten on Venus near the start of the old war after being ambushed and nearly killed. (It could be covered in or just have some pretty big scars.) Turned feral after the tenno that used it due to amnesia that he/she was a tenno and living with the wildlife for so long.
A quest where you have to track him down with Biz helping you would be dope (I love this character).
(This part is just optional) Maybe even blend in some werekubrow stuff with it that people keep spamming in this thread, when the beastmasters transforms his herd goes berserk at the same time and trashes everything.