The office of corrector first appears during the Principate in the reign of Trajan (r. 98–117), for extraordinary officials of senatorial rank, who were tasked with investigating and reforming the administration in the provinces.
To this end, they were entrusted with full imperium maius, which extended also to territories normally exempt from the authority of the Emperor's provincial governors: the free cities of the Greek East, the senatorial provinces, as well as Italy herself.
[1] The full title of these officials, from their institution to the end of the 3rd century, was in Latin legatus Augusti pro praetore [missus] ad corrigendum [ordinandum] statum, in Greek rendered as πρεσβευτὴς καἰ ἀντιστράτηγος Σεβαστοῦ διορθωτὴς [or ἐπανορθωτὴς] (presbeutes kai antistrategos Sebastou diorthotes/epanorthotes).
When he died, his son requested and obtained, after some years, the same title, but later styled himself Augustus; Emperor Aurelian marched East to quash this open rebellion, defeating and capturing Vaballathus as well as his mother (and de facto ruler) Queen Zenobia.
In various municipia, corrector became the title of a permanent single chief magistrate (traditionally there had been collegial systems, e.g. two consules or duumviri), as a Byzantine 7th-century source attests for thirteen cities in the Egyptian province Augustamnica Prima.