I had an all black kitty named Leon who weighed in at 20 pounds. He died a few months ago from diabetes. (He's burried in our yard, in an area we call "Golden Bone."
I still have a male cat named Calvin who is gray and white colored, very similar to Tom of Tom and Jerry cartoons. He and Leon both were my wife's before we got married. Calvin weighs in around 17 pounds. He's very intelligent, playful and affectionate ... except on rare occasions. My wife warned me about him, but I have seen him get aggressive on only two occasions, once at a stray male cat who wandered up to the back door, and once at a tradesman. This cat swelled himself up to the size of a small pitbull (about twice his normal self), and at the same time he got this insane glint in his eyes. His growl was not like any I've ever heard before from him or anything else, and his fangs looked impossibly long for a domestic animal.
I was explaining to a plumber that we had a pair of cats in the house, and that one of them, Calvin, was pretty fierce. The guy said words to the effect that he didn't like cats. Some of his other customers had aggressive cats and they didn't bother him in the least. He said he'd just shove Calvin out of the way if the cat became curious and came around where he was working. As he finished speaking, Calvin went into attack mode and growled at the plumber (6'3", about 250 very solid pounds). He took one look at the cat, turned on his heel and went back outside until I secured Calvin in another room. Smart man!