I've had him since he was 3 weeks old. Basically, the girl i'd got him from lied, told me he was 8 weeks, brought me a litter of kittens, and they all still had blue eyes with film etc. I ended up keeping one. His name is Doug. He's been with us now for almost 6 years. He's the most loving kitten. He is very independant, however he loves human time. Absoletly loves it. With that being said, nothing has changed, but this last week to 10 days he's been aggressive. Literally hissing and trying to bite and scratch me.This cat is outside sometimes...and all i have to do is call him, and 5 minutes later he comes through the kitty door safe at night.
But lately he hasnt been doing this ( he is fixed) and hes being super aggresive?
Is there something i should know?
whats going on with him?!

Simple answer:

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When a cat's behavior changes suddenly, it is highly and most likely they are ill. Vet care is always suggested in the case of sudden change in behavior, especially aggressive. Take him in to the vet, get some bloodwork, etc. done and you will know what's wrong with him.

(My old landlord's dog became suddenly aggressive towards the other dogs, I told them he needs to see the vet, instead they chose to punish him and never let him see the other dogs again and left him in the garage against my repeated suggestion. He died a month later from leukemia. I loved that dog, Simon.

Red-Cross Certified in Dog and Cat First Aid
Retired Volunteer/Foster/Adopt-a-Pet-er for Kill Shelter
Owned by 9 Beloved Indoor-Only Kill Shelter Felines, 6 w/Special Needs >^..^<

He is probably sick or injured.

Since you let him go outside, any number of things could be horribly wrong with him.

If you love your cat, do what's right and keep him inside. They rely on us to keep them safe. There are more dangers during the day than there are during the night - a cat has a better chance of getting away from a raccoon or coyote than a car or a hostile human with a BB gun.

I would suggest taking him to the vet. He could be seriously ill. A friendly cat that suddenly turns mean is generally a cat that doesn't feel like himself.

Add - Maybe nothing can get in, but he can certainly get out.

Possibly sick take him to the vet see what he says

Definitely take him to the vet. He may be in some kind of pain which is making him irritable.

If that's not the problem, then try to think very hard about anything that has changed in the past week. Have someone in the house moved out, or has a new person moved in? Are you or is anyone else in the house gone more (working more, spending more time away from home, went on a vacation, etc.)? Did you get a new pet in the house (cat or dog)? Cats hate change. It's very stressful for them. My female won't "talk" to me for days after I come back from vacation and it took her over a year to get over the new kitten we brought home 5 years ago. If there has been some big change in your cat's routine, that could be the problem. It may take some time for him to get used to it, but he will eventually settle into the new routine.

Something has changed in his catty universe - perhaps a new cat has come into the area and he's taking his frustration out on you or if you have another pet, or someone new has joined your household, it could cause this too.
I'd take him for a check up at the vet to make sure he isn't ill with something, sometimes cats distance themselves from people if they are run down with an infection or small injury. Otherwise it might be a good diea to keep him in for a few days and keep an eye on him.
My cat once got very snappy when she had a stomach infection, and she's usually a cuddlepuss.

Don't listen to people who say cats shouldn't go outside. Unless your cat was living in a sterilised bubble before he put a paw out the door, he's not going to drop down dead from breathing outdoor air. ;)
Though he could feasibly have eaten something (or someone) that made him sick. Go get him a consultation at the vet.

I say keep your cat inside. Lots of things could happen to your beloved kitty ... for example your cat could get run over, could get attacked by a dog and eaten by a Coyote. All those things could happen. I have had my share of ran over cats :( It is very sad I must admit. Maybe like what he/she said above is right .. your little kitty could be injured in some way or sometimes when you let a cat out he can become wild. The answer to your problem is keep your cats inside and just leave your cat alone for a while (but keep him inside) Treat him nicely. If you notice your cat acting funny you should take him to the Vet and quickly.