Søren Kierkegaard is widely regarded as the father of Existentialism. His writings, particularly 'The Sickness unto Death' and 'Fear and Trembling', laid the foundation for this philosophical movement.

Existentialism primarily focuses on exploring the meaning of life and the human condition. It examines the questions of existence, freedom, and authenticity.

Existentialism emphasizes the concept of 'Being-in-the-world', which refers to the interconnectedness of human existence with the world around us.

Martin Heidegger introduced the term 'Dasein' to describe the unique mode of being that characterizes human existence.

Jean-Paul Sartre famously asserted that 'Existence precedes essence', highlighting the primacy of existence over predetermined or fixed essences.

Existentialists use the term 'Bad faith' to describe the state of being inauthentic, where individuals deny their true selves and live according to societal expectations.

Jean-Paul Sartre emphasized the importance of 'authenticity' and 'self-creation', arguing that individuals should take responsibility for their choices and create their own meaning in life.

Existentialists use the term 'Angst' to describe the feeling of dread or anxiety that arises from the realization of the meaninglessness of life.

Friedrich Nietzsche is known for his influential work 'Thus Spoke Zarathustra', which explores themes of self-overcoming, the Übermensch (Superman), and the will to power.

Existentialists use the term 'Alienation' to describe the feeling of estrangement or separation from oneself, others, and the world.

Jean-Paul Sartre is known for his influential work 'Being and Nothingness', which explores themes of freedom, responsibility, and the nature of human existence.

Existentialists use the term 'Nausea' to describe the feeling of nausea or disgust in response to the meaninglessness of existence.

Albert Camus is known for his influential work 'The Myth of Sisyphus', which explores themes of absurdity, meaninglessness, and the pursuit of meaning in a meaningless world.

Existentialists use the term 'Finitude' to describe the state of being aware of one's own mortality and the inevitability of death.

Søren Kierkegaard is known for his influential work 'Fear and Trembling', which explores themes of faith, anxiety, and the nature of religious belief.