Bob from Wigan
When I went to get a cat from the local shelter, I decided that I would call him Jim. When I asked for the cat that had been there longest I was introduced to an enormous black tomcat with a "cat sidhe" chest marking who kept nipping me for attention.
I looked at him, he looked at me and I said out loud "you are sooo NOT a Jim".
So I named him after Bad Bob, the psychopathic albino gunslinger from the film "The Life and Times of Judge Roy Bean". No reason other than that it seemed to fit.
He's quite a mean cat who considers other felines beneath his notice: dogs however, he attacks on sight. He usually wins.