Jerzy Grotowski was a Polish director who lived from 1933 to 1999. He started directing in his home country in the late '50s, then later directed translations of his plays in the West in the late '60s. He was hugely inspired by Stanislavsky, who he thought asked the right questions about the role of acting in theatre. He was also inspired a lot by Brecht and another Russian director named Meyerhold.
Grotowski was well-known for his very experimental style of theatre that he called "poor theatre". He wanted to emphasize the difference between film and theatre, where film took more cues from the realist style of theatre. Grotowski didn't like realism; he made sure to get the actors involved with the audience directly to really show the key differences between film and theatre. His style was called "poor theatre" because he didn't rely on expensive sets or props to perform his plays. Often his actors would have no costumes at all -- they would just wear all black on a plain set. He once said that theatre could be reduced to a single actor and a single spectator, and it would still be theatre.