I have known my cat since he was born, adopted him within months, and had him neutered as soon as the vet would allow it. While he was once rather aloof, he's become a snuggling cat and loves to cuddle with both me and my husband. He's almost six years old now, and we've lived in our current apartment for over two years.

A few months ago, he started becoming aggressive when visitors come over. It doesn't matter if they're completely new or old friends, he reacts the same - hissing, spitting, and even swiping (he's declawed on front paws only). He'll find somewhere to perch that is in the main thoroughfare of the apartment and react nastily whenever anyone gets close.

And when I say anyone, I mean anyone. He hisses and growls at me as if I was a stranger. I can't even get to pick him up and move him as he's so violent. If he calms down at all, he just gets all riled up again the moment someone comes near (within five feet) once more.

Then after the visitor leaves, he's back to his normal, cuddly self. He almost seems offended that I'm distrustful of his intentions at that point.

I don't know what to do. Having friends over is nearly impossible now, since he takes up residence in the high-traffic areas and puts up such a fuss at owner and visitor alike. I'm at my wits' end - what can I do?