Monteverdi - One of the first and most innovative composers of opera. He lived a very productive life, traveling to perform his works all over Italy, for the court, and later on for the first public audiences.
The composer lived a very long life (1567-1643). Like Mozart, Monteverdi was a child prodigy, a child especially gifted in the musical arts. Monteverdi learned to sing and play multiple instruments. He then grew up to be in service to the court of Mantua, quickly growing from simple musician to head conductor. It is here where he composed his first opera, "L'Orfeo", which is considered to be by many to be the first significant opera ever composed.
He then went on to write twenty more operas, but only two others survive. They are called "L'Incoriazone di Poppea"(The Coronation of Poppea), and "Il Ritorno d'Ulisse in patria"(The Return of Odysseus). Only fragments from the other operas survive. It's believed that many of these documents were caught in fire and burned up. Alas!
Monteverdi was crucial in the development of the Baroque from it's Renaissance origins. You say you like Bach, Vivaldi, Mozart, Beethoven? pffft. They are nothing, without Monteverdi.
And listening to the music of Monteverdi, one gets the sense of peace, rhythm. Monteverdi pulls you in with the emotion and keeps you there throughout his entire work, but only if you may have the patience to listen.
Anyway, take a listen to him. You just may introduce yourself to something new.