Despite what you may have seen in that big-budget Hollywood crapfest, Gladiator, Commodus didn't kill his father, Marcus Aurelius, in a sobbing, hysterical rage because the old man didn't want him to be emperor. In reality, the philosophically-inclined Marcus Aurelius carefully prepared his son to take his place:
According to one particularly brilliant review of the movie, "all the stuff about Commodus murdering his father is just a lot of Hollywood BS. In the real world, Marcus Aurelius intended Commodus to be his successor all along. He made him Imperator in 176 AD and gave him the title Augustus the next year (when he was fifteen years old). Father and son ruled jointly until Aurelius died in 180."