>>100350208>>100350228Robert E. Howard created the character of Red Sonya (of Rogatino) for his short story The Shadow of the Vulture, published in 1934. The original Sony/ja is a red-headed mercenary adventurer of Polish/Ukraine origin who in the story participates in the war in Turkey during the reign of Suleiman the Great (most agree the story takes place in 1529). Howard wrote a few warrior-women characters, though there's really only one in the Conan stories (Valeria from "Red Nails"). Sonya had nothing to do with Hyboria whatsoever.
In the 1960s, Howard's stories were being republished under the editorial control of fantasy author L. Sprague de Camp. He took on a policy of taking unpublished manuscripts Howard left behind and completing them, and to rewrite other stories set in other time periods into Conan stories. When the Marvel comic started, this series of Conan novels was basically by far the most well-known version of Conan. As such, when Roy Thomas and Barry Windsor-Smith started up the comic Conan the Barbarian for Marvel comics, they too were quite happy to adapt Howard stories into Conan ones.
And that's how Red Sonya became Red Sonja. "Shadow of the Vulture" became issue #23 of Conan the Barbarian, Sonya became Sonja from Hyrkanian (being the Hyborian version of a slav country to match her origins), and the legend was born. Given how very different Sonja was from Sonya, Marvel managed to copyright her as an original creation, separate from the Conan rights package (which at the time they licensed).
As for public domain: Very thorny area. The Conan stories should be public domain, but due to copyright extenstion the rights are still held by Paradox in the USA. In Europe, however, the rights to Conan and his original stories are now public domain (which is why we're getting a non-licensed Conan Eurocomic). This includes the original Red Sonya of Rogatino.
Red Sonja (marvel) was only copyright registered in the 70s so is not public domain yet.