Theodore 'Theo' Cain was a Werewolf mutt who was first mentioned briefly in conversation in the novella Stalked, he was the father of the main antagonist in that story. He was the patriarch of the Cain clan. He was mentioned by Davis Cain, his great-nephew, in the novella Driven as not being 'the brightest bulb' but also being the 'brightest elder in the clan' as well as hating the Pack for killing his son Zachary and maiming his youngest son Ford. He didn't believe Elena to be the Alpha of the Pack, as most Werewolves don't.
Theo first appears in the Darkest Powers novella Belonging where he kidnaps his grandson Derek Souza under the impression that Derek will eventually see him to be right. He also appears in the novella Driven when his family are being hunted by European supernaturals, he died during an attack.
In Belonging he claims to have had a cousin who couldn't Change and that it 'ripped him right apart', presumably physically.
He has dark hair and green eyes. He is smarter then the other Cains, but that isn't saying much. Derek describes him as "...huge, at least my height, with broad shoulders, graying dark hair and broad bull-dog face."
Derek also describes him as looking quite a look like him and having a mane of hair down to his shoulders. Theo is also described as looking around 50, meaning his actual age would be somewhere around 60 to 70.