Diadumenian was the son of Emperor Macrinus, who reigned from 217-218 CE. Macrinus gained this position after the murder of Caracalla, in which he may or may not have had a part. Diadumenian was first honored with the title of Caesar in 217 CE, which is when this coin would have been minted. It was at this time that Diadumenian also adopted the name Antoninus, in an attempt to solidify his connection to the Antonines and their (fictitious) descendents the Severans. Diadeumenian and his father ruled for less than a year before being ousted by the army in favor of Caracalla's cousin Elagabalus. Andrew Carroll 2011.