Gibbon is essentially reflecting Cassius Dio's own view on Commodus there - he essentially presents Commodus not as a wicked mind, but as a weak one, led astray by the luxury of power. Hence, it's essentially implied Commodus lacked mind-training in the exercise of power. Even though ancient people were very aware that the character of a person could change across the years (this is evident in multiple authors) a different approach (including 'early' signs of ill disposition; see eg. Suet.
Tib. 57; Suet.
Gaius 11); also existed - this is well reflected by the anedoctes reported by the
Historia Augusta.
Of course, Gibbon does not hesitate in dismissing Commodus' later pursuits as the fruit of vice and infamy - that is the impression I get. A more recent approach has carefully analyzed his association with Hercules, and the way he tried to shape his own image after the fall of Cleander (
A Companion to Marcus Aurelius, ed. Van Ackeren, 2012, pp. 239-240):
'Recent scholarship has suggested that Commodus’ behavior in the last three years of his life should be seen as a conscious change in imperial representation, aimed at guaranteeing popular support and, more importantly, endorsement from the armies. Following Marcus’ death, Commodus had started to present himself as the pious son, commemorating his imperial father through coins (
RIC 3, nos. 264–75) and, among other honors, the still extant column of Marcus Aurelius in the (now) Piazza Colonna at Rome (Davies (2000) 42–48). After Lucilla’s conspiracy and the removal of Saoterus, the imperial persona was enhanced by adding Pius to his titulature, possibly linking the emperor to his adoptive grandfather Antoninus, but more likely presenting himself as some sort of
Auctor Pietatis. Following Perennis’ removal in 185, yet another epithet was added, making Commodus Pius Felix – though this change could also relate to the celebrations surrounding Commodus’
Decennales. In any case, the new titulature, which would become a standard part of the imperial titles from Caracalla onwards, presented the ruler as a sort of religious champion for the Empire at large; a substantial step away from the much more senatorial way in which Marcus had presented himself (Van’t Dack (1991)). Consistent emphasis on Commodus’
nobilitas, as the only ever emperor to be able to trace himself back to five imperial (adoptive) ancestors, further showed the supremacy of the emperor. Perhaps the negative reputation of Faustina Minor can be partly seen as a reaction to this claim by her son (Priwitzer (2008) 96–174). Considering these developments in imperial presentation, it may not be surprising that a further step was taken in the very period in which dynastic troubles seem to have been brewing, and Cleander came to the fall. In 189 coins and medallions depicted Jupiter Iuvenis, whose physique resembles Commodus rather than the supreme god, with larger eyes, a smaller beard, and a decidedly less muscular stature (Bergmann (1998) 265). Yet another step away from Marcus’ model of emperorship was made. [...] None of this, however, properly anticipated the emperor’s change in imperial representation in the last three years of his reign. The way Commodus ultimately identified himself with Hercules went beyond what even the most extravagant Roman rulers had done before him, or would do afterwards. From 190 onwards, coins celebrated first Hercules Commodianus and then, from December 191 onwards, even Hercules Romanus Augustus, with several coins showing the emperor on the obverse wearing the lion-skin (
RIC 3, 581, 586, 591; 250–54b, 637–40, 643–44). Now, also, Commodus had himself depicted as Hercules in the (in)famous bust
(above) which is prominently displayed in the Palazzo dei Convervatori in Rome: the Capitoline bust which shows the emperor wearing the lion-skin, and holding the club and the apples of the Hesperides. The pedestal, a globe with zodiacal signs and adjacent cornucopias and kneeling amazons, further emphasizes the emperor’s supreme position (von den Hoff (2005)). This Herculean self-presentation was linked to the renaming of senate, months, cities, and legions after himself. In 192, even the capital was renamed the Colonia Antoniniana Commodiana – probably partly in connection to great restoration works following a devastating fire in that same year (Dio 73.15.2;
HA Commodus 8.6–9, 15.7;
RIC 3, 247, 629). The message must have been clear: only Commodus could continue to guarantee Rome’s greatness, and would protect his realm in Herculean fashion. In similar hyperbole, Commodus re-enacted the divinity’s mythological labors by replicating them in the arena. Dio’s descriptions of these events border on the ridiculous, but as a member of the elite who were increasingly sidelined by the emperor’s behavior, he was hardly an unbiased bystander. Best known is the incident at which the emperor allegedly assembled all those inhabitants of the urbs who had lost their feet, gave them serpent-like appendices, and then slaughtered them with either club or bow and arrows, pretending they were the mythical giants. Only marginally less striking is a previous story that Commodus advertised that he was going to ‘put on’ Hercules and the Stymphalian birds, only for the masses to avoid the arena so as not to get shot (Dio 73.20.2–3;
HA Commodus 9.6). Dio may have smiled at this (though it will have been ill-advised to do so openly), but it did show an emperor who, at least symbolically, gave himself heroic status, far above that of any senator, or indeed the senate as a whole'
