First Appearance: Hulk (UK) #1 (March 1979).
Appearances:
I: Hulk (UK) #1-20, Savage Action (UK) #1-15, Marvel Super-Heroes (UK) #382-395, Daredevils (UK) #6-9, Mighty World of Marvel (UK) v2 #7-15, Savage Sword of Conan the Barbarian Monthly (UK) #85-92, Captain Britain (UK) v2 #1-14, Night Raven: House of Cards.
II: Nocturne #1-4.
Dates Active:
I: 1929-?
II: 1921-1951.

Night Raven was a pulp-style vigilante. More than that, however, cannot be stated with a certainty, because the Night Raven character in House of Cards is different in a number of respects from the Night Raven character in Nocturne--different enough that I'm going to differentiate between the two, if only for simplicity's sake.

Night Raven I is active in 1929 in an unnamed large American city. He is a very athletic costumed vigilante who has no powers. He uses two guns, swings from ropes, stalks the rooftops of his city, marks his enemies (those he doesn't kill) with a bird-brand from his ring (Phantom- and Spider-style). He wears a trenchcoat and fedora; his outfit has a bird-symbol on its chest and his face mask has wing-style eye coverings. He is definitely a killer vigilante. His civilian identity is as an unnamed, white-haired janitor working in the city morgue. He is a Canadian Mohawk and a veteran of World War One; he fought at Ypres as a member of a Canadian unit. He is also somewhat poetic and is knowledgeable about Native American animal lore. He speaks with something of a Canadian accent, and says he left Canada because "Canadians ask questions all the time." He sees himself as a healer, "and a healer must dwell amongst the sick.  And if he cannot save them with either skill or love---then he must ease them gently into death." He seems to have gotten his purpose in life as a teenager from a discussion with his grandfather about the Spirit Raven.

Unfortunately, he's also unbalanced; after rescuing a waitress-singer from criminals a few times he becomes obsessed with her and begins stalking her and spying on her, ultimately killing her once he decides that she can no longer be protected from the "corruption" all around her. He then uses her corpse to bring down a corrupt politician. He may be psychotic; the quote about "a healer must dwell amongst the sick" is delivered to the waitress-singer just before he kills her.

Night Raven II is depicted as having been active in Great Britain since at least the late 1930s or early 1940s, although the text of Nocturne implies that he was active since at least 1921. His shirt and mask are the same, but he has done away with the trenchcoat and hat. He still kills his enemies and brands them, only now he does it with a device located in his glove. On the whole he seems substantially saner than Night Raven I. II works from an underground lair and has a young "sidekick," Scoop Daley. II's archenemies are the crimelord Doctor Hurt and the Asian villainess Yi Yang, who at the time of II's death (1951) says that they had been enemies for "three decades." II is allies with a woman named Mischief; she claims to be a vampire (although demonstrating few vampiric traits). Decades later, when another man takes up the identity of Nocturne, Mischief becomes his ally per the decades-gone-by request of II.

During the 1940s, Night Raven II was the subject of a British radio adventure series; the show's material was provided by II himself, although writer George Jenkins "changed a few names and exaggerated here and there."  II's career ended in 1951. During that summer he fought with Yi Yang and her forces while looking for a mystic artifact called the Looking Glass, which gave glimpses into the past, future, and the souls of others. II obtained it and learned of his own upcoming death the following November from the poisoned bullets of Dr. Hurt. Because of this II used visions of future technology gained from the Looking Glass to build an advanced Nocturne suit, which incorporated the Looking Glass into it. II does not die in 1951, however, but is captured and enslaved by Yi Yang, who transforms him into Hatemare; Dr. Hurt is likewise captured and and turned into Suture. The modern Nocturne, a man named Gray Poldark, used the Nocturne suit to fight against Yi Yang, Hatemare and Suture, finally reawakening the memories of Night Raven in Hatemare. II and Yi Yang seem to die in a later explosion of Yi Yang's headquarters.

Note: The ties of both of these characters to the Marvel Universe are tenuous at best; at one point in Nocturne a police inspector claims that there were no real costumed heroes prior to the events of that title. However, House of Cards has hints that it does exist in the Marvel Universe, and I'm going to count it as such.

I'm informed that one of the Night Ravens appeared in a Nick Fury/Black Widow one-shot some years back, but I have no more information than that. John McDonagh adds that the one-shot is called Fury/Black Widow: Death Duty.