Septimius Severus, in full Lucius Septimius Severus Pertinax was the Roman emperor from 193 to 211 and founded a personal dynasty which converted the Roman government into a military monarchy.
Severus entered the Senate about 173 and became consul in 190. At the time of the murder of the insane emperor Commodus on Dec. 31, 192, he was governor of Upper Pannonia and commander of the largest army on the Danube River. He remained inactive while the Praetorian Guards murdered Commodus’s successor, Publius Helvius Pertinax (March 193) and auctioned off the imperial title to Marcus Didius Julianus. Then on April 13 Severus was proclaimed emperor by his troops. Declaring himself the avenger of Pertinax, he marched on Rome. Julianus was murdered at Rome on June 1, and Severus entered the city without resistance several days later. Severus replaced the Praetorian Guard with a new 15,000-man guard from his own Danubian legions. He temporarily pacified his rival in Britain, Decimus Clodius Albinus, by naming him caesar (junior emperor). In 194 he marched east and decisively defeated another rival, Gaius Pescennius Niger, governor of Syria. Severus then headed westward to confront Albinus, who had declared himself emperor. Albinus committed suicide following his crushing defeat near Lugdunum in February 197.
Birley, A.R. (1999) Septimius Severus: The African Emperor. Routledge.