They were generals that were declared emperor (some successfully and others not so much) by their soldiers during the crisis of the third century. From the death of Alexander Severus to the rise of Diocletian (himself a barracks emperor) there were like 60 legitimate and illegitimate emperors.

Augustus held many titles such as princeps (his main title and where we get prince from) and imperator (basically general, where we get emperor from) as well as consular authority wherever he was. He created the principate.

Diocletian ended the time when the senate had power with his reforms a and reformed the empire into the dominate where it was a true miltary autocracy.

They were generals that were declared emperor (some successfully and others not so much) by their soldiers during the crisis of the third century. From the death of Alexander Severus to the rise of Diocletian (himself a barracks emperor) there were like 60 legitimate and illegitimate emperors.