Though they look completely different and have entirely unique personalities, these two are basically one in the same. Tavii (the humanoid... thing) is the main personality. He's an introverted, anxious, shy, but easily angered fella. He doesn't show off his emotions, so he's hard for anybody to read or talk to. Not a great person to converse with, and is extremely pessimistic most of the time.
Raus (the dog/wolf/demon monster) is a visible projection of Tavii's "inner" personality. Basically everything the man shoves down deep into the folds of his brain in hopes they never see the light of day. Raus can be seen by some, but is invisible to others. It's outspoken, extroverted, lacks a filter, and usually is hard to anger. It is everything Tavii can't seem to get himself to display. Though It is an extension of Tavii, It can take whatever form It pleases, as well as share whatever information It wants (much to Tav's horror I'm sure).

Despite mixing like water and oil, the two have no choice but to get along with one another. But I'm sure there are times where they get extremely frustrated with each other. Raus with Tavii for being an idiot and not expressing much of anything except a scowl, and Tavii with Raus for the beast doing the exact opposite. If they could kill each other in those moments, they would.

This is boring, sorry. G'night.