From out of the earth's dark, forgotten past-- thru the timeless terrors of the Hyborian Age-- stalks the mightiest hero of them all--!
— Original in-house advertisement for the Marvel series.
During the resurge in popularity Robert E. Howard's most popular character enjoyed back in The Seventies, Marvel Comics was quick to take notice of this, and got the license from Conan Productions. In October, 1970, the very first issue of Conan the Barbarian hit the shelves, quickly becoming one of Marvel's top-sellers. Spin Offs soon followed, each becoming popular in their own right, with The Savage Sword of Conan the Barbarian occasionally overtaking its sister title in sales.However, what with certain cinematic failures i.e. Conan the Destroyer and the Red Sonja movie, Conan's popularity waned. During The Dark Age of Comic Books, Conan's main ongoing and Savage Sword were eventually cancelled after a combined 510 issues, to be replaced with other ongoings whose issue numbers barely lasted into double figures. Marvel soon gave up on giving Sword and Sorcery's greatest hero his own title, shunting him off into a few miniseries, the last of which was printed in 2000.Dark Horse Comics then picked up the license in 2003, having previously made several miniseries based on lesser REH properties, such as Cormac Mac Art and Almuric. They took a slightly different approach to the character, putting out one ongoing, with the occasional miniseries on the side.
These comics have all included these examples:
Adaptation Expansion: Pretty much every other Conan comic that wasn't a direct adaptation of an REH story or a pastiche. This became more out of necessity from The Eighties onwards for Marvel, as pretty much every good Conan story had already been adapted. Dark Horse do more or less the same thing.
Canon Immigrant: Red Sonya was a musket-wielding 16th century Ukranian in the Howard story that introduced her, but was retconned into being a Hyborian Age swordswoman in the comic books decades later. Thulsa Doom was a villain in the Kull of Atlantis stories before he was adapted into the villain for The Movie - and even then, he had more in common with the Conan adversary Thoth-Amon (a priest of Set with a fancy for snakes) than he did with his namesake (a semi-immortal necromancer with a skeletal face.)
Depending on the Artist: Conan's build may be leaner or bulkier, as shown by pre- and post-Frazetta covers. In the comics, shown by Marvel's Barry Windsor-Smith and John Buscema. Dark Horse usually go with a happy medium...
Ascended Fanboy: Most people assume Roy Thomas was this. Whilst he was instrumental in getting Conan his own comic, it was Gil Kane who was the big Robert E. Howard fanboy. He did a lot of the artwork for Conan in The Seventies, and he couldn't have been happier.
Continuity Snarl: Inevitable with Conan canon, but an interesting little hiccup occurred in Savage Sword; Recurring villain Ogerd Vadislav was reintroduced in an issue, despite having been swallowed up by an Eldritch Abomination. There was an L. Sprague de Camp story explaining how this happened, and in a later issue of Savage Sword explained this too... in a completely different way to the pastiche, as Marvel didn't have permission to run that story, so they just winged it. Later, they did get permission to adapt the short story, so they ran it, and attempted to explain how Ogerd survived another attack. It worked... kind of.
Gotta Catch 'Em All: Conan the Adventurer became a Crucial Type A and Type B. A talisman of a long-sleeping god was scattered into 6 pieces, and 7 wandering adventurers were promised riches if they found all 6 pieces. Turns out it was the god tricking them so he could initiate a Class 5.
Just Friends: Conan and Red Sonja. During the times they've adventured together it's become clear that Conan is attracted to Red Sonja. Red Sonja, on the other hand, does not feel the same way about Conan.
Outlaw Town: The Abode of the Damned, in the story of the same name, in The Savage Sword of Conan the Barbarian #11 (loosely adapted from the Robert E. Howard story "The Country of the Knife").
Vengeance Feels Empty: Though the main character frequently takes pleasure in brutal revenge, this trope pops up when Conan's ally Zula slays his former master. After Conan asks him how it felt, Zula responds that it simply felt hollow. Interestingly, Red Sonja also mentions this trope during this conversation when she says she was unable to slay the man who ravished her after he had been badly tortured.