Major changes in attitude.. please help.

I have what used to be a very affectionate and friendly feline. He has been with us for about 3 years now. We have other cats as well that he's grown to love and enjoy the company of. He's been fixed and is all up to date on his shots.
Over the past month or so we've been noticing major changes in his behavior and attitude. He yowls at the doors and windows and has attempted many escapes. He now shows hostility toward our other cats and even us. He will growl and yell angrily at everyone and everything that gets in his way of the window or door, where mainly, he now spends his time.
Someone.. anyone. Please help me and my disgruntled feline.

Has a vet check ruled out any health problems? Cats are very good at hiding their illnesses, and sometimes the only thing that you can notice is a behavioral change.

is there a cat maybe visiting the door/window?


I am having similar problems with one of my own cats.. except he isn't showing any attitude towards people.. mostly just his brother.

No, I'm afraid we haven't had a vet check recently. But I will look into that. Thank you.
And there may be other cats outside taunting my dominant alpha male of the house, but none that we have whitnessed yet.
Thank you again for all of your help

I would bet on an outside cat catching his attention. This sounds like re-directed aggression.