This was someone's pet (he has been neutered) that got lost or was abandoned. He started staying on our front porch and following us as we walked our dog.
Our dog doesn't like many cats, but tolerates Pepe. We let him come into the house last winter and now he comes in everyday and sleeps on his bed in the garage at night (the garage is heated and cooled).
If you look at that expression, you can see that he thinks he's the master and he's probably right.