Bishop73

Answer: After Commodus murdered his father, he demanded Maximus' loyalty, which the latter refused. This I think made Commodus realise Maximus was aware of his late father's wish. So he decided to get rid of the threat by ordering for Maximus execution including his family.

Answer: Emperor Marcus Aurelius told his son, Commodus, that Maximus would be his successor and the next Emperor instead of his son. This angered Commodus and he killed his father before the Emperor could name his successor. Commodus then ordered for Maximus to be executed, partly out of hatred and fear that Maximus may have already been told that Marcus was going to name him as his successor. Out of jealousy, hatred, and anger, Commodus also ordered Maximus' wife and son to be killed. In real life, Marcus granted Commodus the rank of Imperator and made him co-Emperor before his death and there was never a question who the successor would be, plus General Maximus is a completely made up character and never existed in real life. So this hatred of Maximus and fear of not being Emperor was made up just for the movie, so it's hard to say exactly what threat Maximus may have been if left alive.

Bishop73