Demetrios Poliorketes (Greek Δημήτριος Πολιορκητής Dēmḗtrios Poliorkētḗs, Latin Demetrius Poliorcetes; * c. 336 BC; † 283 BC in Apamea) was a Macedonian general and diadochal ruler from the Antigonid dynasty.
Demetrios was one of the most prominent representatives of the eventful diadochal wars that broke out among Alexander the Great's generals after his death in 323 BC. Demetrios himself was not a general of Alexander, but is nevertheless counted among his successors (Diadochi) together with his father Antigonos I, since he died before Lysimachus, Ptolemy and Seleucus. Among his rivals, Demetrios stands out in many respects. He fought in Asia as well as in Europe, conquered Athens twice and won the double battle of Salamis. At the same time, he failed in the great siege of Rhodes and was mainly responsible for the defeat in the decisive battle of Ipsos in 301 BC. In the process, he led the largest armies as well as fleets and built the most formidable ships and siege engines of his time. His nickname, "the city besieger" (Poliorketes), refers to his military skills in besieging and conquering cities.
Together with his father Antigonos I Monophthalmos, Demetrios was the first Diadoche ever to assume the title of king in 306 BC, claiming sole succession to Alexander the Great. Having grown up in Asia, he was influenced by an oriental image of rulership, which he celebrated in the capital of Attic democracy with lavish festivals and an extensive personality cult. In this way, he himself became one of the first representatives of a new type of ruler who shaped the era of Hellenism. As king over Macedonia, which he brought under his control for a few years, he ultimately failed, however, and only his son was able to establish stable rule over the country.