The first existentialist

The  first  existentialist  was  not  Sartre,  though  he  coined  the term.  Nor  was  it  Kierkegaard  or  Nietzsche,  though  most  of the  textbooks  say  so.  Nor  was  it  even  Pascal,  though  he foreshadowed  half of Kierkegaard  and  was  the  first  to  write about the fundamental existential experience of cosmic anxiety and meaninglessness.  It was not even Saint Augustine,  whose Confessions  stands  out  as  the  profoundest  example  of depth psychology and existential autobiography ever written.  It was not even  Socrates,  who  alone among  the philosophers  totally existed  his  philosophy.
Rather,  the  first  existentialist  was  Solomon,  or  whoever wrote  Ecclesiastes.  Here,  some  twenty-five  hundred  years before Sartre’s Nausea, Camus’ The Stranger, Beckett’s Waiting for  Godot,  or  Kafka’s  The  Castle,  we  have  the  fundamental experience  and  intuition  of  each  of  these  modern  classics, expressed  more  candidly,  directly,  and  artlessly  than  ever before  or  ever  again.

Peter Kreeft, Three Philosophies of Life: Ecclesiastes, Life As Vanity Job, Life As Suffering Song of Songs, Life As Love