Male Cat aggression

I have 6 cats. 4 females and 2 males. 1 of my male cats, has recently become aggressive toward the other cats lately. I've seen him spray on our back porch, but not in the house. The porch is screened, so they don't go outside. He was neutered when he was a kitten, before I got him.  He's around 3 or 4 years old, I believe. He has never been aggressive or pushy with the other cats until recently. All of my cats are spayed/neutered rescues. Any ideas?

[AnnieBrooke]

Sounds like he is trying to move up to Alpha cat.  

[AnnieBrooke]

You know, marking his graffiti tag over others' tags, gunning for the sheriff, strutting his stuff at the dance.  If he can do it with pee, he doesn't have to do it by fighting.  Sounds like the girls aren't buying it much.

[FridaP]

Yeah, the alpha cat (female) passed in March. Everybody seemed fine with not having a sheriff, just lots of deputies. I guess he decided the job was open, he'd fill it.