Newcomer Summer Glau, is a premier ballerina from San Antonio, TX. She has appeared on Angel in the episode "Waiting in the Wings," which was directed by creator Joss Whedon. 

He liked her so much, that he wanted to cast her to be in his new series, Firefly as one of the title characters River. She has also appeared in several commercials on the East Coast and this fall she is reprising her role of River in the feature film Serenity. 

Source: dragoncon.org