Shar-Teel Dosan is an amazonian warrior woman who enjoys humiliating male adventurers by challenging them to duels and defeating them. If she is defeated in a duel by a male member of the player's party, she is impressed and grudgingly pledges to join the group. Extremely aggressive and bloodthirsty, Shar-Teel has a strong hatred of males, and the Flaming Fist mercenary company in particular. At the end of the game, it is revealed that Shar-Teel is the daughter of Angelo Dosan, a lieutenant in the Flaming Fist who is also secretly in the employ of Sarevok.
Source: Wikipedia, "List of Baldur's Gate characters", available under the CC-BY-SA License.