Who introduced the 'Dramatic Monologue' ?

Dramatic monologue, a poem written in the form of a Speech of an individual character; it compresses into a single vivid scene a narrative sense of the speaker’s history and psychological insight into his character. 

This form is chiefly associated with Robert Browning, who raised it to a highly sophisticated level in such poems as:
- My Last Duchess
- The Bishop Orders His Tomb at St. Praxedes Church
- Fra Lippo Lippi,” and “Andrea del Sarto
Source: An ABC OF English Literature - Dr. M. Mofizar Rahman