You can find a complete list of the characters with their descriptions if you go to the link listed below.
The most important characters are listed below:

Anagnos: sends Annie to the Keller home from Perkins Institute
Aunt Ev: meddling visitor who contacts Perkins for the Kellers
Doctor: tries to comfort the Kellers after Helen comes out of her high fever
Captain Keller: Helen's father who battles with Annie Sullivan the whole time about her technique with Helen
Helen Keller: The deaf and blind main character who is highly intelligent, but has not been disciplined until Annie comes
James Keller: Helen's step-brother who is jealous of the attention paid to Helen
Kate Keller: Helen's mother who feels guilty about Helen and has to allow Annie to discipline Helen
Annie Sullivan: the "miracle worker" who must teach Helen discipline in order to teach her how to survive in the world

There are a few other characters and more descriptions of the ones I've given if you go to the link below.

http://www.enotes.com/miracle-worker/6502