Caravaggio (Michelangelo Merisi da Caravaggio) was well known for his incredible use of chiaroscuro (http://www.enotes.com/homework-help/who-chiaroscuro-42543).
His oil paintings are primarily of biblical and dramatic nature, popular in that time period (late 1500s), and worked in Rome early in his career when there was a high demand for paintings to fill new churches and palazzos.
Because of his realistic style, and effective, dramatic use of light/dark he was (and still is) incredibly popular and influential.
He killed a guy too! Supposedly.