The influential French philosopher known for their ideas on existentialism is Jean-Paul Sartre. His works, particularly "Being and Nothingness," explore themes of freedom, responsibility, and the inherent meaninglessness of life. Sartre posits that individuals must create their own essence through actions, emphasizing the idea that "existence precedes essence." His concept of bad faith examines self-deception and the avoidance of personal responsibility. Sartre's philosophy has profoundly impacted literature and social thought, making him a central figure in 20th-century existentialism and humanism, influencing countless writers and philosophers.