Jean-Paul Sartre wrote No Exit in 1944, an existentialist play originally published in French as Huis Clos (meaning In Camera or "behind closed doors") which is the source of the popular quote, "Hell is other people." (In French, "l'enfer, c'est les autres"). The play begins with a Valet leading a man into a room that the audience soon realizes is in hell. Eventually he is joined by two women. After their entry, the Valet leaves and the door is shut and locked. All three expect to be tortured, but no torturer arrives. Instead, they realize they are there to torture each other, which they do effectively, by probing each other's sins, desires, and unpleasant memories.
"Existentialism," by Wikipedia