The Parallel Lives are primarily concerned with exploring various modes of eudaimonia, as Plutarch mines the lives of illustrious Greeks and Romans for moral exempla and offers them up to his audience for contemplation and imitation. In contrast to his usual practice, Plutarch offers the Demetrius and its Roman pair the Antony as explicitly negative examples. These men, who are “conspicuous for badness,” habitually engage in behavior this is to be rejected, not imitated. Demetrius is capable of great virtues, but his life provides a paradigm of how not to live. The ruinous state of Hellenistic historiography, however, places a historical burden on Plutarch’s moralizing biography that it was manifestly not designed to bear. Indeed, Plutarch’s Life is the sole continuous account of Demetrius’ career, and provides the only literary evidence for many of the events from the Battle of Ipsus in 301 to Demetrius’ death in 282. Despite all this, there is no full-length commentary on the Demetrius in any language. This thesis represents an attempt to fill that gap. The commentary is not merely a survey of relevant scholarship, but offers many original contributions to the study of Hellenistic kingship and ruler-cult, the politics and propaganda of the Successors, and Demetrius’ pivotal role in the remarkable advances in naval technology and siegecraft for which the period is justly famous. While the body of the commentary firmly grounds Demetrius’ career in the historical context of the early Hellenistic period, the historiographical introduction illuminates the didactic ethics that shape Plutarch’s biographical project, and confronts the vexed question of his sources.