Little is known of the early life of Charles McNider. In 1941, McNider was an accomplished physician and researcher working in New York City. Late one evening he was called upon by police to treat a mob informant by the name of Brown,who had run afoul of local Mafioso "Boss" Maroni. As McNider tended Brown, a local gangster threw a grenade into the room and the resulting explosion killed Brown, his nurse, and the attending police officer. McNider survived, but the explosion left him blinded for life. He abandoned his medical practice at this point, devoting himself to writing crime exposes. His nurse, Myra Mason, became his personal assistant.

McNider was meditating in his study one fateful evening when an owl broke a window, startling the physician. In his haste, McNider loosed his bandages and discovered that, in the darkness, he had the ability to see. However, upon turning on the lights, he was blinded once again. His vision was only functional in the absence of light. Energized by this discovery, McNider studied a variety of lenses in an attempt to find a kind that shielded him from the light and heightened the infrared in the darkness. He also adopted the owl who had led to this discovery, naming him Hooty. Eventually, McNider perfected his lenses and decided that his ability to see in absolute darkness would give him an advantage in battling the criminal element. He devised a series of chemical explosives called "blackout bombs," which produced thick clouds of black smoke in which only he could see. McNider also devised a costume and code-named himself Doctor Mid-Nite.

Doctor Mid-Nite's first act as a "mystery-man" was to track down the criminal that had led to his blindness: "Boss" Maroni. After saving the life of an informant critically injured in a Maroni reprisal, Doctor Mid-Nite ambushed Maroni in his lair. Cutting off the power to his home left the crime lord and his lackeys in complete darkness, allowing Mid-Nite to thrash them as they fumbled blindly. With Maroni in jail, McNider worked harder in his writing and promoting anti-crime messages. Eventually, McNider chronicled some of his own exploits as Doctor Mid-Nite (All-American Comics #25).

As a mystery-man, Mid-Nite was an inveterate foe of organized crime. McNider also resolved to battle crime through other media, by writing scathing editorials and detective stories based on figures in organized crime, which also provided an effective cover for his knowledge of Dr. Mid-Nite's activities. Indeed, throughout the 40's, Myra Mason appeared blissfully ignorant that that the two were one in the same (tho some criminals came close to figuring it out  - All-American Comics #88). He also continued making contributions to medical research and serving as a consultant to the military (Wonder Woman vol. 1 #234-235).