Commodus also had a passion for gladiatorial combat, which he took so far as to take to the arena himself, dressed as a gladiator. The Romans found Commodus's naked gladiatorial combats to be scandalous and disgraceful.[12] It was rumoured that he was actually the son, not of Marcus Aurelius, but of a gladiator whom his mother Faustina had taken as a lover at the coastal resort of Caieta.[13]

In the arena, Commodus always won since his opponents always submitted to the emperor. Thus, these public fights would not end in death. Privately, it was his custom to slay his practice opponents.[14] For each appearance in the arena, he charged the city of Rome a million sesterces, straining the Roman economy.

Commodus raised the ire of many military officials in Rome for his Hercules persona in the arena. Often, wounded soldiers and amputees would be placed in the arena for Commodus to slay with a sword. Commodus's eccentric behaviour would not stop there. Citizens of Rome missing their feet through accident or illness were taken to the arena, where they were tethered together for Commodus to club to death while pretending they were giants.[15] These acts may have contributed to his assassination.

Commodus was also known for fighting exotic animals in the arena, often to the horror of the Roman people. According to Gibbon, Commodus once killed 100 lions in a single day.[16] Later, he decapitated a running ostrich with a specially designed dart[17] and afterwards carried the bleeding head of the dead bird and his sword over to the section where the Senators sat and gesticulated as though they were next.[18] Dio notes that the targeted senators actually found this more ridiculous than frightening, and chewed on laurel leaves to conceal their laughter.[19] On another occasion, Commodus killed three elephants on the floor of the arena by himself.[20] Finally, Commodus killed a giraffe, which was considered to be a strange and helpless beast.[21]

http://en.wikipedia.org/wiki/Commodus#Commodus_the_gladiator

(http://www.autoadmit.com/thread.php?thread_id=2553948&forum_id=2#25460553)