Between the reign of Marcus Aurelius and Diocletian, what type of rulers were usually in control of Roman Empire?

Between the reign of Marcus Aurelius and Diocletian, what type of rulers were usually in control of Roman Empire were generals who were declered emperors by the army especially in so called 'crisis of third century' 234-283 during that period there was more than 25 emperors

Generals of armies and legions.