List the most important philosophers of existentialism.

Existentialism is a term used to define philosophers from the late 19th and 20th century, who felt that the conventional philosophy is too abstract and remote from real human experience. Therefore, their philosophy started from human individual, and describes its disorientation in absurd and meaningless world. There is not, actually, the precise definition of existentialism, but Soren Kierkegaard is considered to be the first existential philosopher, despise that he never used that term. The second most important philosopher of existentialism from 19th century was Friedrich Nietzsche. Existentialistic way of thinking could be also found in the works of great Russian writer, F.M. Dostoyevsky. The one to coin the expression "existentialism" was Jean-Paul Sartre, and important existentialistic thinkers and artists from 20th century were: Albert Camus,  Samuel Beckett, Franz Kafka, Eugène Ionesco, Luigi Pirandello and Joseph Heller.