Derringers were invented, or at least popularized, by a man named "Deringer" (note the single "r"). The original Deringer was a small, handy, single barrel, .41 caliber percussion pistol that could be easily concealed. A classic hide-out gun. John Wilkes Booth used one of these to assassinate Abraham Lincoln. When other manufacturers wanted to capitalize on the burgeoning popularity of these small pistols, they called their generic pistols "derringers," and that is where the extra "r" came from."