Viola Spolin, who died in 1994, can probably be considered as the American Grand Mother of Improv. She influenced the first generation of Improv at the Second City in Chicago in the late 50`s, as her son, Paul Sills, was one of the co-founders.
Spolin developed new games that focused upon creativity, adapting and focusing the concept of play to unlock the individual`s capacity for creative self-expression. These games (several of which have become classics) are described in Improvization for the Theatre .
Read more about Viola Spolin on www. spolin.com , or check out the Hall of Fame at the Improv Page , where you can find a couple of articles about her and her work.