Gregório de Matos e Guerra (December 23, 1636 – November 26, 1696) was a famous Portuguese Baroque poet from Colonial Brazil.

Although he wrote many lyrical and religious poems, he was better known for his satirical ones, most of them criticizing the Catholic Church, earning him the nickname "Boca do Inferno" (Hell's Mouth).

There he became friends with poet Tomás Pinto Brandão (1664–1743) and married D. Michaella de Andrade, and, two years later, was appointed as a magistrate in Alcácer do Sal.

A malcontent, he criticized everyone and everything: the church, government and all classes of people, from the rich and powerful to the lowly pauper, sparing no race or profession.

Tradition says that a few minutes before death, he asked two Catholic priests to come at him and stand each one aside of his body; thus he described himself as "dying between two thieves, like Jesus Christ in his crucifixion".