From Melissa Marr's website:

From Biblical origins: Seth was the third son of Adam and Eve; his name means "appointed." In an alternate etymology (Greek), his name means "dazzle."

Characteristics: Blue-black hair, which "[falls] over his face when he move[s], like tiny arrows pointing to pronounced cheekbones." Seth favors tatoos and piercings. He has steel bars in his eyebrows and a ring in his lower lip. He also wears black nail polish.

Seth is at least six feet tall, as he's a foot taller than Aislinn (and she is not described as unusally tall). His body type is lean, with his muscles well defined.

All the female characters in the book comment on Seth's good looks.

Personality: Aislinn calls him 'the epitome of calm.' He's also outgoing, as his circle of friends is wide -- in fact, Aislinn met him through mutual friends, and while she was most attracted to him because he lived in a railroad car, she grew to like him for himself.

Although he's had a number of girlfriends, he doesn't have the reputation of being a heartbreaker.

Seth is open-minded with eclectic tastes. Although he doesn't understand what is going on with Ash, and isn't convinced she's right about it being fairies, he is determined to help her. Over and over, Seth challenges the rules, the assumptions over what can and can't be done and works diligently to preserve Ash's right to be her own person.

Likes: Reading and research (Seth is a self-proclaimed research god), making art in various mediums -- has plans to go to art school some day. He reads voraciously, creates art in various mediums,

History: Sometime after he graduated high school, his parents went away to do misionary work, leaving him everything they had. He used some of the money they left him to buy a train and convert it to a sutiable living situation.