"‘Was Wild Bill one of the quickest shots?’ I ventured.
"‘Fair,’ smiled Cody, and I too smiled to hear a man say that Wild Bill was a ‘fair’ shot. But this was Buffalo Bill speaking, and he spoke as one with authority.
"'"Bill" was only a nickname we gave him, you know.’ I didn’t know, but nodded. ‘His real name was James B. Hickox, and we got to calling him "Wild Bill" because when we were all boys together there were four "Bills" in the wagon train, and we had to sort them out somehow. Jim Hickox was always popping away at everything he saw move when on guard at night over the stock, so we sort of got to calling him "Wild" Bill, and that is how the name came to him. They called me "Buffalo" Bill because I had that buffalo contract with the U. P. and got down over 4,250 for meat. I have forgotten what became of the other two "Bills."’
"‘How did Hickox get so many men?’ I asked. "‘Well, Bill was a pretty good shot, but he could not shoot as quick as half a dozen men we all knew in those days. Nor as straight, either. But Bill was cool, and the men he went up against were rattled, I guess. Bill beat them to it. He made up his mind to kill the other man before the other man had finished thinking, and so Bill would just quietly pull his gun and give it to him. That was all there was to it. It is easy enough to beat the other man if you start first. Bill always shot as he raised his gun. That is, he was never in a hurry about it; he just pulled the gun from his hip and let it go as he was raising it; shoot on the up-raise, you might call it. Most men lifted the gun higher, then threw it down to cock it before firing. Bill cocked it with his thumb, I guess, as it was coming up into line with his man. That’s how he did it. But he was not the quickest man by any means. He was just cool and quiet, and started first. Bill Hickox was not a bad man, as is often pictured. But he was a bad man to tackle. Always cool, kind, and cheerful, almost, about it. And he never killed a man unless that man was trying to kill him. That’s fair.’ It was, and so I agreed.
http://www.usgennet.org/usa/topic/preservation/bios/zane.htm