Short answers, pulled from the story.
Marcus Opellius Macrinus was born in Caesarea, now known as Cherchell, within the Roman province of Mauretania Caesariensis. His family belonged to an equestrian class and traced their origins to local Berber tribes.
On the 11th of April 217 Macrinus proclaimed himself emperor and assumed all imperial titles without waiting for Senate approval. The army backed his claim immediately while the distant Senate remained powerless to intervene.
Macrinus revalued Roman currency by increasing silver purity and weight of the denarius from 50.78 percent to 57.85 percent. This change mirrored Severus' fiscal policy from 197 to 209 AD while veterans kept their high pay but new recruits received lower wages set by Severus standards.
During the battle near Immae on the 8th of June 218 Macrinus deserted the field and fled to Chalcedon before being recognized and captured. He was executed in June 218 in Cappadocia after injuring himself trying to escape captivity, with his head sent to Elagabalus as a trophy.
The Senate declared Macrinus and his son enemies of the state immediately after news arrived of their deaths and ordered all portraits destroyed. Their names were stricken from inscriptions and papyri across the empire while Roman soldiers rebelled against Macrinus also destroyed all works and possessions belonging to him.