Tintin! TV Tropes says, "...even compared to the (very chaste) standards of the other characters of the series. It's even difficult to remember him talking to a girl." Indeed. All I remember is some guys ransacking his apartment and chloroforming him. Oh, childhood memories. And another character whose sexuality (or lack thereof) I have pondered:
Rorschach! From Watchmen (book and movie). He was my favorite character in Watchmen, which is saying a lot, since he's a misogynistic right-wing nutcase. He's repelled by anything sexual, although this probably has to do to his past; his mother was a prostitute and in the book, we're shown Rorschach as a child walking in on his mother with a client. Much like Dexter (of the books and TV show), the irregularities of these characters' minds and their antisocial behaviors obscure any real knowledge of their sexualities. TV Tropes brought up another Watchmen character that I had never considered as possibly ace. The site says, "Of all the characters in Watchmen, Ozymandias is the best reflection of real life asexuality. In a graphic novel which features the sexualities of all the major and several of the minor characters, Ozymandias's is not ever mentioned or displayed in any way. Rorschach, on the other hand, comes across as
Ozymandias is not a reflection of real-life anything-- he's just as bizarre as Rorschach, albeit in a different way. However, he could come across as a really physically fit, technologically skilled version of Sherlock Holmes. Ozymandias is billed as the smartest man in the world, and thinks the world of himself as well. Like Holmes, another man who is way too smart (and knows it), Ozymandias found intellectual pursuits more stimulating than sex or romance.
It's worth noting that on the TV Tropes page of potentially asexual characters, men outnumber women at about 10:1. This seems in keeping with my own observations of pop culture, however, we all know that there are more women than men on AVEN. As always, media lags behind real life, if it isn't ignoring it entirely. And again, I'm left asking where my fictional girls are at.