Jean-Paul Sartre was a French philosopher who was a key figure in the philosophy of existentialism. Some of his major ideas included that humans have radical freedom and are condemned to be free. People are responsible for their own actions and cannot blame external factors like their upbringing or environment. Sartre also argued that through our choices we create our own essence rather than having a predetermined purpose or nature. His works such as Being and Nothingness and Existentialism is a Humanism explored these concepts of individual freedom, responsibility, and the need to create our own meaning in life.