Francesco Cavalli
Cavalli lived at the time that opera had just been invented by Jacopo Peri.  Claudio Monteverdi composed the first really good operas.  Cavalli became the most important Italian writer of operas in the middle of the 17th century.  His operas use small orchestras, unlike those of Monteverdi, who was writing for the court in Mantua where there was lots of money for big orchestras.  Cavalli had a good sense of drama and he wrote lovely melodies.