Unlike in Gladiator, Marcus Aurelius fully intended for his son to be emperor. Commodus was made Augustus and joint emperor with his father in 177 AD. Also unlike in Gladiator where he is portrayed as spoiled and detached from the military campaigns, Commodus spent two years (178-180 AD) leading Roman troops with his father in campaigns along the Danube River.
Commodus also actually reigned twelve years, rather than less than the six months in the movie. His older sister Annia Lucilla was in fact part of a failed plot with her second husband to assassinate Commodus in 182 AD, exiled and eventually executed. However, the rather incentuous relationship of the film is unlikely, since she was twice married. Unlike in the film, Commodus was initially interested in governing, but after a few years, he did stop taking interest in the day-to-day matters of government and left it to his Praetorian prefects.
Like in the film, Commodus did have an unusual fascination with the Roman Coliseum and the gladiatorial games. He actually fought many times in the arena as a gladiator, either killing helpless animals or gladiators. After he proved to be nearly mad by wanting to rename Rome to Colonia Commodiana (City of Commodus), another conspiracy was led by Praetorian prefect Quintus Aemilius Laetus. He did not die in mortal combat in the Coliseum, although his assassin was his wrestling partner, Narcissus.
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