Cassander (kəsăn´dər), 358–297 BC, king of Macedon, one of the chief figures in the wars of the Diadochi. The son of Antipater, he was an officer under Alexander the Great, but there was ill feeling between them. After his father's death, Cassander engaged in vigorous warfare against Antipater's successor as regent, Polyperchon. He was successful, and by 318 he had a preponderant influence in Macedonia and Greece. Alexander's mother, Olympias, challenged this and put Philip III, Alexander's half-brother, and many others to death. Cassander pursued her, crushed her army, and condemned her to death (316). Later, to strengthen his claim to the throne, he married Alexander's half-sister, Thessalonica, and in 311 he murdered Alexander's widow, Roxana, and their son. He resisted the efforts of Antigonus I to rebuild the empire and was one of the coalition that defeated Antigonus and Demetrius at Ipsus in 301. Secure in his position, he founded the cities of Thessaloníki and Cassandreia (on the site of Potidaea) and rebuilt Thebes.