"Monet was making extra money at age 15 drawings caricatures which he signed O. Monet. He sold these at a local store for 10-20 francs a piece. They were often depictions of his teachers and his fellow students would purchase them." (source)
He was born in November 1840 in Paris. The second son of a grocer. Started school when he was five. Eventually joined the army, got sick with typhoid, was pulled out to go to art school. Married Camille, had children. She died of tuberculosis. He became an impressionist. He liked to paint pictures of controlled nature (gardens and the like). He remarried. He got cataracts at one point which affected his art work. He died of lung cancer at age 86. You can find his complete biography here.