Degen was a Nayabaru - an established guard (Hesh) at the Tain pens. He trusted Terenyira's judgement about Ne͡ivat'va's value and rapidly treated her as he would an equal - albeit certainly a strange one.
He appears a few times in the early chapters of A Thread Between The Stars: Kaleidoscope, Kirigami and Quipu, and is mentioned at the very end of the Catalyst chapter.
Personality
Degen held no blanket hate for the kavkema in his heart, though he never stopped to question the way Hesha treated the creatures, and gladly participated in the perpetuation of the status quo. For him, those rituals were part of the new order of things, and on an abstract level, he took much joy out of that the predators were now at the whim of their ancestral prey. That said, he was wholly lucid of his instinctual fear of the kavkema, and more alert of the creatures for it.
Like all integrated Nayabaru, he was an atheist, though well aware of several kavkem mythologies in theory. That said, he would have baulked at having to describe any - no doubt in part because he took care in not necessarily believing everything kavkema said, reminding himself occasionally that they were both capable and willing to lie.
History
Degen was proud to serve at the Tain pens as Tain was known for keeping its city borders “meticulously safe”1) Before the events of A Thread Between The Stars, he had dealt with several kavkema before, to the point of snatching up various fragments of their mythology and their tongue (Kendane͡ivash). he had not met the Karesejat personally before.
When Tavor brought Ne͡ivat'va into the pens (nameless as she was at the time), his preconceptions of the world were thoroughly uprooted, a matter he took in decent stride and handled with professionalism (quite unlike Toben). The point of greatest confusion came from Terenyira's request to treat Ne͡ivat'va with respect and to leave her be unless she tried to harm someone. Since she never did harm anyone, Degen consistently kept his hands off her.
It was Degen who, driven by curiosity, began a conversation with the nameless Ne͡ivat'va, which ended in her giving herself her name. (He tried to puzzle out the meaning with his limited knowledge of Kendane͡ivash to no avail, until he caved, asked, and was told that it means “She who was forgotten”2).)