The so-called “golden period of the empire” consisted of the rule of the emperors: Nerva, Trajan, Hadrian, Antoninus Pius and Marcus Aurelius (96-180 CE). At that time, the choice of the ruler was made by designating the person considered the most worthy and suitable, and it was possible due to the lack of direct heirs.
However, Marcus Aurelius (penultimate of the Antonine dynasty) had a son whom he did not consider worthy of succession. Nevertheless, he could not designate him, in order to prevent the unleashing of rivalry for the throne after his death and the outbreak of conflicts and disputes.
Cassius Dio mentions that Emperor Marcus was clearly disappointed with Commodus, whom he provided with proper education, and despite placing his hopes in him, he was not worthy of assuming the highest office in the Empire.