Public Domain Super Heroes says this about the character, The Duke of Darkness: “The Duke of Darkness was Paddy Sullivan [emphasis by me, Pappy], a police officer from an unnamed American city. When he was killed in the line of duty, Danny [another emphasis of mine] discovered that he continued to exist as an 'Earth-bound spirit.' He decided to continue fighting crime as the Duke of Darkness.”
The bringing up the two civilian names of Duke of Darkness (from his former mortal existence, of course) is because at the bottom of the entry for Duke of Darkness the anonymous writer for PDSH says this: “Many sites state ‘Danny’ as the character's real name however, this [Danny name] never appeared in a public domain story.”
Tsk tsk. Looks like some editing is needed. I depend on that site, so I'm just giving those fine folks at the PDSH a friendly heads-up.
It wasn’t like the Duke of Darkness set any records for longevity. He made but a few appearances and then was gone. Each comic book he appeared in had a different name, and each lasted one issue. I am supposing my old theory that they were published by someone who sold (or used) their paper ration at the end of World War II to cash in on the comic book market. Finally, the Public Domain Super Heroes site gives us this final note: “Even though he's a ‘ghost,’ he is able to be knocked out by a bump on the head such as in his first adventure.” Maybe there is a learning curve, watch your head, for people finding out they have died and are now a spirit.
Created by Sam Cooper and John Giunta, and presumably written and drawn by them for this first Duke’s story from K.O. Komics #1 (1945):