Søren Kierkegaard (1813-1855) had notable contributions in ideas such as Leap of faith, Existential despair, Existential philosophy, Angst, Authenticity etc. [1]<p>[1] <a href="https://en.wikipedia.org/wiki/S%C3%B8ren_Kierkegaard" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/S%C3%B8ren_Kierkegaard</a>