Red Sonja was based on Red Sonya of Rogatino, a character from Robert E. Howard's short story "The Shadow of the Vulture" (The Magic Carpet, January 1934). Red Sonya was a sword-and-pistol-wielding supporting character of the late Renaissance. Red Sonja debuted in Marvel's Conan the Barbarian #23 (cover-dated Feb. 1973). Roy Thomas created a new origin story and transposed the timeline from the 16th century of Howard's original Red Sonya, to the Hyborian Age, another Howard creation, in order to have the comic-book Red Sonja interact with Conan the Barbarian. Thomas also used, to a certain degree, elements of Howard's character Dark Agnes de Chastillon.
The thing that sets Red Sonja apart from all her contemporaries is her look. The bright fiery red hair and, of course, her iconic metal chain bikini. In her first two appearances in Conan the Barbarian, issues 23 and 24 (1973), she is dressed a little more conservatively, in a long-sleeved mail shirt and short pants of red silk, a style that did not last long. Spanish artist Esteban Maroto submitted an uncommissioned illustration to Roy Thomas when he was editing the magazine Savage Sword of Conan where he redesigned the character and for the first time showed her wearing what would become her famous costume, the silver "metal bikini", which resembled other fantasy costumes that other Maroto heroines sported in the 1970s. The illustration was printed for the first time in Jim Steranko's magazine Comixscene #5 in black and white. It was reprinted in Savage Sword of Conan #1, and in Marvel Treasury Edition #15 colored but poorly reproduced, and finally restored and colored by José Villarrubia as an alternative cover for the Dynamite Entertainment edition of Red Sonja #2. Maroto drew her in this costume for a double page spread illustration in Savage Tales #3 and then for her first solo adventure in Savage Sword of Conan #1, and John Buscema drew her in this costume in the same magazine.
Buscema drew her again in this costume in issues 43, 44 and 48 of Conan the Barbarian (1974) and Dick Giordano drew her in the armor in the first issue of Marvel Feature Vol.2 (1975) before Frank Thorne took over at issue 2 (1976). The "bikini" proved popular with fans becoming well known through the paintings of Boris Vallejo and others, and would become Sonja's signature look.
Some classify Red Sonja as a nothing more than a sex object in comics, something for fans to ogle at and drool over. But Red Sonja is more than that, she is a strong, fierce warrior who can hold her own and doesn't need help from no one. She is a tough warrior while also being a bombshell. She can kick your ass while also looking good. Red Sonja shows that women aren't helpless damsels but they can be the ones out saving the day and making the world better. Red Sonja emphasizes what it means to be a heroine in comic books.