Frank Griffin (Doctor)
Dr. Frank Griffin was the younger brother of Dr. Jack Griffin, the infamous first Invisible Man. Like Jack, Frank was a chemist. He was a close friend of the Radcliffe brothers, who allowed him to house his laboratory within the Radcliffe Colliery. After Michael Radcliffe was murdered and Geoffrey Radcliffe framed for it, Frank took a big chance when he replicated his brother's duocane formula and administered it to Geoffrey during a visit to his jail cell, allowing him to become invisible and escape.
While the invisible Geoffrey hid out, Frank tried to make an antidote to the formula before his friend went insane just as Jack Griffin had. Frank's efforts were hindered however, both by the meddling Willie Spears and the well-meaning but bothersome Inspector Sampson, and the fact that all the animals he tried the antidote on died. Ultimately, after Geoffrey was shot by Sampson, Frank was forced to give him a blood transfusion to save his life, discovering that all that was needed to undo the invisibility formula's effects was fresh blood (a technique later hit upon by the ill-fated Dr. Peter Drury).
He shared a name with his grandnephew, Frank Griffin.