The infamous dirty old man of Azumanga Daioh, Mr. Kimura is a classical Japanese teacher, who freely admits that he became a teacher out of his love for highschool girls.
While he looks fairly normal in the beginning, after admitting to the above vice his mouth is left permanently wide-open for the rest of the series. Kimura's behavior is quite creepy and erratic, doing such things as asking for a glass of water from the pool that the girls have been swimming in so that he can drink it, or running around the corridors screaming as an advertisement for the classroom cafe that the girls set-up. While this sort of behavior has earned him the disgust of the female students and faculty, some of the boys have expressed admiration for his shameless honesty.
Despite this, he never makes any move to have any sort of sexual or physical contact with any of the girls, and outside of his perverted nature, is a fairly morally scrupulous man. He is seen picking up other people's litter so as to recycle it, giving generously to charity, and donating money to a shrine while praying for world peace. Much to the shock of his students, Kimura is revealed to be married to a gentle, attractive woman ( Mrs. Kimura), with whom he has a daughter.
Of all the girls, Kimura seems most fond of Kaorin, who is far from enthusiastic about his admiration. After her, Kagura is the student that he appears to harrass most. He is also quite possibly the originator of the "mai waifu" meme.