It's German-born film star Conrad Veidt.
He's one of my favorite early cinema actors. Perhaps his most memorable role was Cesare the "somnambulist" in
The Cabinet of Dr. Caligari. Veidt was a regular fixture in German expressionist films of the 1920s.
In 1933, Veidt came to Hollywood and began working in American cinema. He was Universal's first choice for the role of Dracula, but when Tod Browning took over as director he decided to give the role to Bela Lugosi, a genuine ethnic Romanian who had already been playing the part of the vampire in a popular stage production.
Viedt did a number of horror/thriller/adventure-type movies in the 1930s, but he's best known to American audiences as the Nazi Major Heinrich Strasser in the movie
Casablanca. He played a few roles as Nazi heavies in early '40s Hollywood films, which was ironic because he was in real life a staunch and very vocal anti-Nazi and though he himself was not Jewish, he was married to a Jewish woman and had fled Germany to escape the Nazi regime.
Some time in the late '20s, Veidt took to wearing a monocle due to failing eyesight in his right eye. Monocles were often worn back then by artists, statesmen and members of the upper classes, and were considered to be a mark of class and aristocracy. Veidt's monacle wearing became so well-known that he once remarked, "I was not born wearing a monocle!" It's likely that the character Colonel Klink from the TV series
Hogan's Heroes was created as an homage to Veidt.
I chose this particular photo of Veidt because I feel it pretty much fits my own visual impression of the nick "Colonel Panic".