Hugin and Munin both first appeared in Thor #274 and were adapted from mythology by John Buscema and Roy Thomas. The characters subsequently appeared in Thor #276, 300, 338-339, 341-344, 371, 373-375, 379, 381, 478, and 484, spanning between Oct. 1978 and July 1987. They also appeared in Avengers #310, Thor #45, Thor: Man of War #1, Marvel Pets Handbook #1, Thor and the Warriors Four #2, Official Handbook of the Marvel Universe A-Z #14, Thor and the Warriors Four #4, Thor #618, Loki #3, Thor #620, The Mighty Thor #1, Fear Itself #1, Journey into Mystery #622, The Mighty Thor #2, Fear Itself #2, Journey into Mystery #629 and Avengers Origins: Thor #1.
Munin and Hugin are brothers and the ravens of Odin. He sends them out into the Nine Realms each day to learn what was transpiring. They are the ones that tell Odin about the coming of Ragnarök. There was a time when the birds went into Muspelheim after Odin sent them to travel to the demon's domain and discover the secret of their origin. Odin carved runes into their claws so they might pass beyond any barrier. When they get to their destination, Surtur senses their arrival and the fight begins.
The Death of Hugin
watches as Hugin races for his life and falls to the bridge. Heimdall takes Odin to his home beside the bridge where Munin lies and Odin and Munin speak for a while, Munin telling Odin what he wanted to know. Munin returns to the royal throne room with a black feather and gives it to Balder, who is now king since Odin's death. Seeing the single black feather as a bad omen, he calls Heimdall and has him watch over Asgard while he investigates his hunch about the feather. Munin guides Balder through the endless desert until they find one of the Sisters of Fate and Balder asks her to grant him water from the Well of Life. She gladly gives it to him, but tells him to use it wisely, as it is a gift that can only be given once. Taking the vial of water, Balder explains that Munin went down into the realm of Muspelheim with his brother Hugin, but Munin came back alone. Pulling out the single feather Munin gave him, Balder pours the water on it and resurrects Hugin. With the two birds reunited, Balder turns to thank the Sister of Fate, but finds that she is gone. With their quest over, Balder orders the birds to return with him to the city of Asgard.
Several Asgardians, including Sif and Fandral have fallen in the battle against Fin Fang Foom. Balder has also fallen, but is conscious enough to tell Hugin and Munin to get the Elixir he got from Wyrd, and give it to Mick and Kevin. The birds retrieve it and give it to the boys, who hand it off to Balder and help restore the fallen gods.
Marnot
In addition to Hugin and Munin, Odin had a third raven, Hescamar, later renamed Marnot. Marnot's first appearance was in Thor #2, where he arrived in Hel to retrieve Thor from Hela so Thor could redeem himself for Jake Olson's death. When Hela hears that Marnot plans to take Thor away, she goes to stop him, but Marnot grabs her by the throat, revealing that his power is enough to stop even her. When Marnot revives Thor, it is in Jake Olson's body, but Thor has no memory of Jake's life, so he has to bluff his way through it when he returns to Earth. Thor plans to leave Jake's body, but Marnot tells him he does not recommend it before telling him he knows all he needs to know and leaves. When Marnot tells Thor the story of the Dark Gods to talk him out of attacking them, Thor decides to cast all of the Dark Gods out of Asgard anyway. After the defeat of the Dark Gods, Marnot was revealed to really be Hescamar and was later killed by one of Hela's Cyphers, who took the form of Keith Kincaid. He appeared in 10 issues of Thor, spanning from August 1998 to September 1999, and then again in one issue of Thor #37.
In the Ultimate Marvel imprint, the ravens appear in , a prequel to The Ultimates which explores the origins of Thor in a backstory more faithful to the Norse mythological stories. They appear alongside Odin and are killed during Ragnarök.
In other media
Television
Hugin and Munin appear in the animated TV series in the episode "".
Film
Hugin and Munin can be seen briefly in the live action 2011 Marvel Studios film Thor. They make an appearance in the beginning at Thor's coronation, perched on Odin's throne and in Odin's room while he is in the Odinsleep.
They appear in 2012's The Avengers when Thor takes Loki from the S.H.I.E.L.D. Quinjet and they argue on the mountain top.