What if Marcus Aurelius' co-emperor Lucius Verus ( http://en.wikipedia.org/wiki/Lucius_Verus ) hadn't died and instead outlived Marcus Aurelius. Could he stopped Commodus' madness and kept the Roman Empire stable?
well wouldn't Verus rule as emperor rather than Commodus but i doubt he would be able to influnence him an more then Marcus Aurelius but i think that Commodus would marry Verus's daughter, which could lead to Verus appointing his grandson emperor rather than Commodus if he lives long enough