Toonopedia.com, I see that only his incarnation in the 1950s and '60s is mentioned, and his history from the 1940s is not. It is true that they seem to be two characters with the same name and appearance, both drawn by Bob Powell and his studio. The Man in Black (also called Fate, or Kismet) of the 1950s (see the link below) is a character who observes people at that moment when they have arrived at a fork in the road, and are deciding which one to take. The character we are showing today is also called Mr Twilight, or Death. In this incarnation he guides the spirits of the recently deceased to an afterlife. The afterlife is even referred to in one panel as Valhalla, although it doesn’t sound, from Mr Twilight’s description, to be the Viking Valhalla.
There is a bad guy, Dr Hideki, who is obviously Japanese, but the story was published in 1947, and the late unpleasantness of war against the Japanese is not mentioned. People die, and Dr Hideki brings 'em back to life. In this story we are supposed to root for them to die and be taken to their reward by Mr Twilight. If it sounds confusing...well, I guess it is. If anything, it probably isn’t a standard comic book plot. It is beautifully illustrated by Powell, who did his usual superb job, no matter how screwball the story.
From Green Hornet Fights Crime #34 (1947):
As promised, here is the Man in Black from 1957. Just click on the thumbnail.