(Spoiler warning goes here.)
Hoshino Ruri (seiyuu: Minami Omi) is the cynical-beyond-her-years computer operator in the sci-fi/parody anime Martian Successor Nadesico as well as the central character of Nadesico the Movie: Prince of Darkness.
Though the series began with her as a side character, she soon became a large part of M.S. Nadesico's popularity with her dry commentary about the general idiocy of the crew (herself included) and general cuteness.
Ruri's main job on the Nadesico was to operate the ship's computer, Omoikane. Since the ship controlled many of it's functions itself, she spent a lot of her time using Omoikane for video games, and experiencing and commenting on the social environment (her stint on the Nadesico was her first time out in the "real world," after living her whole life on a "brain farm"). Her commentary usually included phrases like "baka," "minna baka," "baka-baka," and "hontoo baka."
In the Nadesico movie (a different storyline, like most anime crossovers/sequels go), she's the ship's captain. She's significantly more grown-up in the movie - less sarcastic, more feeling, but still innocent and sweet. The character quickly became a lot more popular with male fans, resulting in lots of posters, wall scrolls, shitajiki, etc. (featuring the new Ruri in silky red dresses and such ^_^;). Plenty of hentai doujinshi too, of course.
Ruri-ruri's popularity has grown to such an extent that she was voted #1 anime heroine of all time in Newtype's 15th anniversary issue "Hiroin Ninki Best 30." Not bad for a 11 year old (16-ish in the movie).