For almost a thousand years, Autokrator was the title of the Roman Emperors. Emperor literally meant those that had power of Imperium, originally given to the roman commanders in the field.
Other titles include Augustus, and the first one to assume that title was Julius Cesar nephew and adopted son, Octavius.
Octavius was granted the title of Augustus on January 16, 27 BCE, and in some ways this can be considered the official first day of the Roman Empire, and it’s last day May 29, 1453 CE, after 1425 years, 4 months and 13 days (there is no year 0) with the death of Autokrator Constantine IX.