Stray cat owns family

We don't know who owns this cat, but this cat seems to own us. Someone in the neighborhood recently put a collar on him that reads 'Rocky, AKA the visitor cat', with a disconnected phone number. Ella named him Jackie before the collar appeared, so Jackie he remains. He answers to just about anything though, and comes out of no where when they call him. He then struts into the house like O'Malley The Alley Cat, and pretty much takes over. He had the girls at meow, and me at hopping on our bed while Matt was napping.