Pietro Antonio Domenico Trapassi, better known by his pseudonym of Pietro Metastasio, was an Italian poet and librettist, considered the most important writer of opera seria libretti.

A libretto is the text used in, or intended for, an extended musical work such as an opera, operetta, masque, oratorio, cantata or musical. The term libretto is also sometimes used to refer to the text of major liturgical works, such as the Mass, requiem and sacred cantata, or the story line of a ballet.