Red Sonya was a character created by Conan author Robert E. Howard.
Red Sonya of Rogatine appeared in The Shadow
of the Vulture story set in Vienna during the Turkish
siege of the city in the 16th century. Russian by birth, Sonya was
a tall red-headed cutlass and pistol wielding lassy - and nothing
like the Hyborian swordswoman of this film or indeed the comics
and novels that gave birth to it.
Marvel story writer Roy Thomas simply took the original Red SonYa,
changed the name to Red SonJa, and placed her into
the Hyborean age as a female foil for the very popular Conan stories
that he was penning.