Who Is The Father Of Existentialism?

Jean Paul Sartre is often credited with being the father of the existntial philosophical school of thought.  However, the title should actually rest with Soren Kierkegaard,a Danish philosopher (1813-1855).  He believed that philosophy wasted too much time thinking about the so called realities of the world, or the 'essences'.  He felt that nothing could be objective, that all we have in life is subjective truths.  For example, the statement 'To kill is wrong' is not always correct, since it is acceptable in times of war etc, so the statement is not objective, it is subjective, becaus eit depends on the circumstances of the time.  
So, he argued that what we are, is what we do.  We cannot be guided by society, we can only act authentically and be true to ourselves.  So we should choose how to act for ourselves, not be driven by society.  In this way we can accept resonsibility and make our own choices.  This, in essence is actually the foundations of existentialism.