Marcus Fabius Quintilianus (c.35–c.100) was a Roman rhetorician from Hispania, widely referred to in medieval schools of rhetoric & in Renaissance writing. In English translation, he's usually referred to as Quintilian, altho the alternate spellings of Quintillian & Quinctilian are occasionally seen, the latter in older texts.
The only extant work of Quintilian is a 12-volume textbook on rhetoric entitled Institutio Oratoria (Institutes of Oratory), published around 95. This work deals not only with the theory & practice of rhetoric, but also with the foundational education & development of the orator himself, providing advice that ran from the cradle to the grave. An earlier text, De Causis Corruptae Eloquentiae (On the Causes of Corrupted Eloquence) has been lost, but is believed to have been "a preliminary exposition of some of the views later set forth in Institutio Oratoria" (Kennedy, 24). In addition, there are two sets of declamations, Declamationes Majores & Declamationes Minores, which have been attributed to Quintilian. However, there is some dispute over the real writer of these texts: "Some modern scholars believe that the declamations circulated in his name represent the lecture notes of a scholar either using Quintilian's system or actually trained by him" (Murphy, XVII-XVIII).