Ace Hanlon

This isn't necessarily restricted to the end of the Frontier era. I believe some of Mark Twain's stuff from his California days mentions such pretenders and "would-be bad men." Charlie Russell also mentions a few, and he was active in the later 1880s as a horse wrangler. I've also seen reprinted newspaper accounts from the Kansas cattle towns (circa 1870s) that mention a few of these types.

There were a number of fairly (in)famous people who had the reps as "pistoleers" as they were known back then, when they had very little on which to base their legend.

Johnny Ringo comes to mind as one of that type, who was all flash with little substance.

Then there were the guys like Chris Madsen, Bill Tilghman and Heck Thomas who actually were deadly with their guns but didn't care to boast about it so as to draw attention to themselves.

Bat Masterson was credited with killing at least a dozen men, but in reality he may have only killed two. He turned down a US Marshal's appointment because he feared kids who had been "spoon-fed on dime novels" would come to test themselves against him.

A lot of these guys went out of their way to develop the fearsome personas so nobody wanted to test them face-to-face... and they were gunned down from ambush, like Ben Thompson.

Luke Short earned reknown for being a gunman of considerable prowess because a lucky shot from him hit "Long Haired" Jim Courtright's thumb during a confrontation. Before Courtright could switch hands, Short shot him dead.

He coasted on that shot for the rest of his life...which wasn't that much longer, actually.

Sure there were, BM. In all ages and for most all things.

Depends on the town, too. If there's been a rise of lawlessness, some jerk waving a gun around & spoiling for a fight could reasonably find himself on the wrong end of a Winchester, or strung up by a vigilance committee.