The title was also claimed by Carus' other surviving son, Carinus, but Diocletian defeated him in the Battle of the Margus.
Diocletian's reign stabilized the empire and marks the end of the Crisis of the Third Century.
Diocles' parents were of low status, and writers critical of him claimed that his father was a scribe or a freedman of the senator Anullinus, or even that Diocles was a freedman himself.
The first forty years of his life are mostly obscure.
Born to a family of low status in Dalmatia (Roman province), Diocletian rose through the ranks of the military to become roman cavalry commander to the Emperor Carus.
After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor.
He lived out his retirement in his palace on the Dalmatian coast, tending to his vegetable gardens.
His palace eventually became the core of the modern-day city of Split in Croatia.
Most recently, Emperor Carus and his sons had ruled together, albeit unsuccessfully.
He appointed fellow officer Maximian as Augustus, co-emperor, in 286.
Diocletian delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors.
Although effective while he ruled, Diocletian's tetrarchic system collapsed after his abdication under the competing dynastic claims of Maxentius and Constantine, sons of Maximian and Constantius respectively.
The Diocletianic Persecution (303–11), the empire's last, largest, and bloodiest official persecution of Christianity, did not destroy the empire's Christian community; indeed, after 324, Christianity became the empire's preferred religion under its first Christian emperor, Constantine.