Diogenianus was a Greek grammarian and lexicographer from Heraclea Pontica in Asia Minor. He lived during the 2nd century CE, under the Roman emperor Hadrian. Beyond this, the details of his personal life and education are not recorded.

His work focused on compiling and summarizing earlier dictionaries. He is credited with two main works, though neither survives intact. One was a lexicon of Attic words and phrases. His more significant work was a comprehensive general dictionary, which was itself a condensed version of an even larger lexicon by Pamphilus of Alexandria. This compilation became an important resource for later scholars.

Diogenianus's primary historical importance lies in his role as a vital link in the chain of Greek scholarship. His comprehensive lexicon served as a major source for Hesychius of Alexandria, who compiled his own famous dictionary centuries later. According to modern scholars, Hesychius's work is a crucial source for understanding ancient Greek vocabulary, including rare words and fragments from lost literature. Therefore, although Diogenianus's own writings are lost, his work indirectly contributed to preserving a vast amount of linguistic knowledge for future generations.