Jacobo Peri was an Italian composer and singer working in Florence. He had worked in churches, then later in the Medici court as a singer and keyboardist, then later a composer. At that time, there was a general feeling among Florence's intellectuals that the art of their time was inferior to that of the ancient Greeks, so they became obsessed with trying to recreate Greek tragedy. So with the support of Jacopo Corsi, a music patron, and the help of poet Ottavio Rinuccini, Jacopo Peri wrote Dafne. According to modern scholarship, it was a long way off from what the ancient Greeks would have recognized, but instead it spawned a whole new form that would last for then next 400 years. Drawing on a new development at the time, Peri established recitatives, melodic speech set to music, as a central part of opera.
Though opera seems to be largely limited to Italians and Germans, I think it is important because it firmly establishes the idea of bringing in many media to form a greater whole. Dafne was basically a play that was written by a composer and a poet, combining elements of all of those media.
History of Opera Timeline
A Brief History of Opera
Jacopo Peri from Wikipedia