What title did Roman emperors use for the commander of the Praetorian Guard?

The Roman title for the commander of the Praetorian Guard was Praetorian Prefect.

The prefect, known in Latin as praefectus praetorio, originally commanded the emperor’s household troops. Over time, the office became one of the most powerful positions in the imperial administration, especially because the Praetorian Guard protected the emperor and operated close to the political center.

Praetorian prefects could influence succession, court politics, and military affairs. Under later emperors, the office also acquired major judicial and administrative responsibilities. The title should not be confused with the Urban Prefect, who was responsible for the administration and order of the city of Rome.