Who were 2 famous existential philosophers?

Soren Kierkegaard (1813-1855) was a Danish philosopher, theologian and psychologist. He is considered by some to be the father of existentialism both theistic and atheistic. He wrote that faith is not a decision based upon evidence because the level of evidence required is unavailable. He argued that doubt is an element of faith and it is impossible to find any objective certainty about religious doctrines such as the existence of God. Christian doctrine is inherently doubtful and therefore a Christian must rely on faith to make the commitment to believe. Kierkegaard stressed the importance of self and the self's relate to the world as being grounded in self reflection and introspection. He wrote under pseudonyms that represented his different ways of thinking.

John Paul Sartre (1905-1980) was a French existentialist philosopher, playwright, novelist, university professor, political activist, screenwriter and literary critic. He is the leading figure in 20th century existentialism. His main idea is that we are condemned to be free. The universe is meaningless and man is a lonely being

There is no creator and as for our own actions and behavior, "We are left alone without an excuse". His works were prohibited by the Roman Catholic Church. One of his most famous lines is, "L'enfer, c'est les auto" which is usually translated as, "Hell is other people".