Mister spends most of his time alone, as cats are wont to do. He doesn't mind though. Playing the hero is really more Dresden and Mouse's thing. Mister much prefers to perch himself on a bookshelf and watch the brownies do their work. Or nap in front of the fire. Or sneak into the basement to knock the talking skull around. Or, go out and explore the city. He's never been one to be cooped up for long. He likes to take in the sights and the sounds of the city that makes up his world and he prefers to do it alone.
Some cats are social, Mister is not. Even with other cats he doesn't like to mingle and make friends. Now, the lady cats, that's another issue. He always enjoys the company of a cat in heat, but once the fun is over and he's passed on his marvelous genes, he's off again. Mister would not win any Father of the Year awards, but he's a cat and such things are below him. He tolerates Mouse because he has to. The dog somehow wormed his way into Dresden's heart and is now part of the "family". Mister made sure his dominance was established when the dog was young. There would be no chasing of this Mister, no way. It worked too. Mister is firmly at the head of the household.
He lets Dresden think he's the Master, but that's not true. Mister is his own master and his own he will remain.