We have a cat that wanders around the neighborhood. This morning around I found my one year old cat fighting with the stray. This is not their first encounter. The stray cat is mean and growls and hisses at me. Now around the evening on the same day, my cat is growling at me when I pet him and growls if I go to pick him up. He is normally one of the most friendliest cats. I have separated the cat(the mean) and two other cats. Should they be together?

He may have gotten hurt, or he's just in a bad mood from the fight. He may have small scratches or bruises you can't see, that make it painful for you to pet or pick him up.

If he lost the fight, then his ego will be bruised. Just like a human, a bruised ego from being shown up can cause irritability and a general desire to be left alone.

How long has this been going on?

It's called redirected aggression. He wants to rip apart the mean cat, but takes this feeling out on you. Keep your cat(s) away from the mean one.

Are your cats neutered?

Yes, both my male cats are neutered.

Only about two days. His refusal to eat started today.

Two days isn't long enough to consider it a true change in personality. Give it a few more days.