Sartre was a French existentialist philosopher, author and critic. Famous for Being and Nothingness, he was a leading figure in 20th century French philosophy and a principal spokesman for the existentialist movement in post-war France.
Jean-Paul Sartre (June 21, 1905-April 15, 1980) was born in Paris to Jean-Baptiste Sartre, an officer of the French Navy, and Anne-Marie Schweitzer, of Alsatian origin, and a cousin of French Nobel prize laureate Albert Schweitzer. Sartre's philosophy possesses a clarity and force that captured the spirit of his times in a more powerful way. His prominent contemporaries include his lifelong partner Simone de Beauvoir, and Maurice Merleau-Ponty.
The central theme of all existentialist philosophies is the claim that 'existence precedes essence.' Sartre conveys the view that a person first exists without purpose or definition, and since there is no God, finds him/herself in the world, and only then, as a reaction to experience, an individual can define the meaning of his/her life.
It is the opposite of the argument presented by Aristotle in his Ethics that a person is created to fulfil a purpose or goal, and that fulfillment of a life consists in striving towards that goal.
Sartre's radical freedom has weighty consequences, since everyone is responsible for everything one does. A person cannot, in Sartrean existentialism, make excuses or defer responsibility to either a divine being or human nature: to do so would constitute a self-deception.
In effect, Sartre's existentialism "condemned an individual to be free" which exhibits a strictness of optimism as his detractors accused his philosophy of. One positive point is that Sartre's philosophy has placed the destiny of an individual within himself.
Biographical Dictionary, edited by Una Mcgovern, Chambers, 2002
Philosophy, the Great Thinkers, by Philip Stokes, Capella, 2007