The "Headless Rider" of Durarara!!, Celty Sturluson is in truth a horse-riding Dullahan from Ireland, who came to Japan to retrieve her head.
Celty Sturluson is an underground worker who lives in Ikebukuro. Known as the Headless or Black Rider, she seems to be one of the greatest urban legend in the city. Actually, she is an ancient fairy from Ireland, known as one of the Dullahan. She came to Japan in hope of finding and getting back her lost, or stolen, head.
Her also famous black motorcycle is actually her horse, which she named Shooter. Even though she possesses no head, she have unknown sensors, as Shinra theorized, that makes her have the all senses except taste. She is also very overpowered for a human, although her strength is inferior to the likes of Shizuo Heiwajima and Simon Brezhnev. She seemingly able to manipulate darkness, or an unknown dark substance that continuously seeps from her neck like smoke. She can also turn them to weapons like her classic scythe and many other things.
Celty lives with Shinra Kishitani, the son of the man that found her in a ship. With him, she is able to live a bit of a normal life while being a courier as Shinra is an underground doctor. The two of them are couples, although they weren't until later on in the series.
Celty wears black rider outfits mostly, and wears a yellow cat helmet. To communicate, she uses a PDA, but can also speak telepathically, but rarely does it.
Years ago, Celty Sturluson, a Dullahan lost her head. Dullahans are fairies who throws a tab of blood to anyone who gazes at them. When she woke up, Celty had lost most of her memories, and decides to search for it with her horse. She felt the presence of her head and decided to pursue the thief. Her search lead her to a ship heading for Japan. She turned her horse into a motorcycle and stowed away aboard the ship. Meanwhile a little boy name Shinra Kishitani discovered her and told his father about her. As the years went by she stayed with Shinra and took on the job as a deliverer, at least until she finds her head (and, with it, her identity and purpose).
Celty Sturluson was created by Ryohgo Narita for the purpose of being the heroine in the light novel series Durarara!!. She makes her first appearance in both the first chapter of the light novel and first episode of the anime adaptation. She is voiced by Miyuki Sawashiro in the Japanese version and Kari Wahlgren in the English Version.
The official Crunchyroll subtitles for Durarara!! episode 4 shows her name as "Celty Sturlson" (Celty may come from the term "Celtic," since we're talking about Ireland here)-- however, her screen name shown on her laptop is "Selty Sturlson," so the official romanization is still somewhat up in the air.
Celty - much of irony - has the most normal and human personality compared to most Durarara!! characters. Although she seems cold and stoic as a fairy, she became more of a jolly, optimistic, and confident person - probably due to her interaction with humans, in which Shinra has great contributions. Celty is a member of the Dollars, and is one of the few who knows who's the real leader and founder of the organization.
Celty is pretty acquainted with pop-culture, as she loves watching TV, playing video games, DVDs, and going chat online. She also has her insecurities - concerning how people would react if they found out who and what she really is - and phobias - her fear or the extraterrestrials and the Traffic Police, especially from Kinnosuke Kuzuhara - which is a comedic element in the series.
As the series went by, she became more open to some people beside Shinra, such as Shizou, Mikado, and Anri, due to them being able to not just accept the paranormal, but of them being able to accept her.
At first, Celty seems to have feelings for Shinra, who's head-over-heels inlove with her, but is unsure whether it is really love or not. She also have a some kind of habit in hitting Shinra on the gut whenever he mentions his love or his love relationship fantasies with her. She also gets angry whenever Shinra dismisses her need for her head. Later on, she accepts her lost head and is now in a happy relationship with Shinra.