Check the catalogue or browse the shelves at 937 (Ancient Rome) and check the index for information about Commodus.
Use JSTOR and the HIstory Reference Centre to find articles about Commodus in History journals.
Commodus as Hercules, from the Musei Capitolini, Roma (Capitoline Museum, Rome). Image by Slices of Light x Flickr.
The Gladiator by 
Emperors of Rome: the Monsters by 
Emperors of Rome by