Diocletian was Emperor of Rome from 240 - 311, when he abdicated due to illness. As Emperor he was known as Gaius Aurelius Valerius Diocletianus but was born with the name Diocles, near Spalatum (modern Split) in Dalmatia. His father was the scribe for a wealthy senator and may have been a freed slave.
Diocletian rose through the ranks of the Roman military, eventually becoming Emperor along with a junior co-ruler Maximian. His importance as a figure in Church history is as the instigator of a particularly harsh persecution of Christians which produced many martyrs. He increased the cult of the Emperor, calling himself the son of Jove, and tried to revive the worship of the Roman gods.
In about 297 an edict was made that all soldiers and Imperial officials must sacrifice to the gods - failure to do so resulted in dismissal.
In 303 Diocletian ordered the destruction of all churches and and the burning of all Christian Scriptures. Further edicts in the same year ordered that all Christian clergy be imprisoned and tortured until they agreed to sacrifice to the Roman gods.
In 304 Diocletian made his final order for the persecution of Christians. All Christians, both lay and clergy, who refused to sacrifice to the Roman gods were to be executed.