Keith Johnstone is widely regarded as the father of modern improvisation.
He began his work at the Royal Court in the 1950s, where he was directing plays and looking for ways to make his actors more alive, more responsive - more human. He and his cast felt that the improvisations they were doing to solve these problems were much more entertaining than the play they were meant to be rehearsing, so they began staging those instead.
Pretty soon "The Theatre Machine" was touring around Europe. Keith would direct a band of actors in improvised scenes and audiences went crazy. No-one had ever seen theatre like this before.
However, in the UK, Keith faced a problem. Censorship was still in force and the law required that the Lord Chamberlain's office approve scripts for all performances. This was clearly not possible for the Theatre Machine. Keith wrote the Lord Chamberlain a letter suggesting that one of his "lackeys" sit by the side of the stage during their shows and ring a bell if anything occured of which he disapproved, but no reply was forthcoming. When the University of Calgary offered him a professorship, he took it at once.
In Calgary, he founded the Loose Moose Theatre and invented Theatresports which spread rapidly all over North America and most of Europe. It was a direct inspiration for Whose Line Is It Anyway and is still the world's most popular form of public improvisation.
Keith still teaches, directs, writes plays and inspires fresh generations of improvisers. His books, "Impro" and "Impro For Storytellers" are still in print and highly recommended.