Gaius Aurelius Valerius Diocletianus was born in Diocles. Born to a Dalmatian family of low status, he rose through the ranks of the military to become cavalry commander to the emperor Carus. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was acclaimed emperor by the army. A brief confrontation with Carus' other surviving son Carinus at the Battle of the Margus removed the only other claimant to the title. With his ascension to power, he ended the Crisis of the Third Century.

Main Roman Coin Book and Other References:

RIC = Mattingly, Harold    The Roman Imperial Coinage
BMC = Coins of the Roman Empire in the British Museum
RSC = Seaby, H A    Roman Silver Coinage
RCV = Sear, David R    Roman Coins and Their Values
Cr = Crawford, Michael    The Roman Republican Coinage
SB = Sear, David R    Byzantine Coins and Their Values
S = Coins of England and the United Kingdom
WW = Wildwinds.com (reference & attribution site)