The renowned philosopher Jean-Paul Sartre's theories on existentialism were significantly influenced by his experiences, particularly during World War II. His time as a prisoner of war and his observations of human struggle shaped his understanding of freedom and responsibility. Sartre believed individuals create their essence through choices, a notion reflected in works like "Being and Nothingness." His existentialist ideas advocate for authenticity and emphasize the isolation inherent in the human condition, concepts he engaged deeply with, drawing from his own life's challenges and complex realities.