Michelangelo Merisi, known as Caravaggio, was an Italian painter active in Rome, Naples, Malta, and Sicily between 1592 and 1610. His paintings conveyed an amazing realism (he often used working-class people as his models) and a stunning use of light and dark. He's also known for his violent lifestyle: at one point he had to flee Rome after killing a man in a fight.

Rome has many works by this amazing artist, several of which can be seen for free in churches:

Church of San Luigi dei Francesi - three paintings (The Calling of St. Matthew, The Inspiration of St. Matthew, and The Martyrdom of St. Matthew)

Church of Santa Maria del Popolo - two paintings (The Conversion on the Way to Damascus, and The Crucifixtion of St. Peter)

Church of Sant' Agostino - one painting (The Madonna del Loreto)

Galleria Borghese - five paintings (The Madonna of the Serpent, David with the Head of Goliath, Boy with a Basket of Fruit, St. Jerome Writing, and Young Sick Bacchus)

Palazzo dei Conservatori (Capitoline Museums) - two paintings (The Fortune-Teller, and a version of Young St. John the Baptist)

Vatican's Pinacoteca (picture gallery) - one painting (Deposition from the Cross)

Palazzo Corsini - one painting (another version of St. John the Baptist)

Palazzo Barberini - three paintings (Judith Beheading Holofernes, St. Francis in Prayer, and Narcissus)

Galleria Doria Pamphilj - three paintings (Rest on the Flight into Egypt, a version of Young St. John the Baptist, and The Penitent Magdalene)