Alexander IV Aegus (in Greek, Aλέξανδρος Aιγός — 323–309 BC) was the son of Alexander III of Macedon and the princess Roxana, of Bactria.

Because Roxana was pregnant when her husband died and the gender of the baby was unknown, there was dissension in the Macedonian army regarding the order of succession. While the infantry supported the baby's uncle, Philip III (who was both epileptic and illegitimate), the chiliarch, or vizier Perdiccas, commander of the elite Companion cavalry, persuaded them to wait in the hope that Roxana's unborn child would be male. The factions compromised, deciding that Perdiccas would rule the Empire as regent while Philip would reign, but only as a figurehead with no real power. If the child was male, then he would be king. Alexander IV was born in August, 323 BC.

After a severe regency, military failure in Egypt, and mutiny in the army, Perdiccas was assassinated by his senior officers in June 320 BC, after which Antipater was named as the new regent at the Partition of Triparadisus. He brought with him Roxana and the two kings to Macedon and gave up the pretence of ruling Alexander's Empire, leaving former provinces in Egypt and Asia in control of the satraps (see diadochi). When Antipater died in 319 BC he left Polyperchon, a Macedonian general who had served under Philip II and Alexander the Great, as his successor, passing over his own son, Cassander.

Cassander allied himself with Ptolemy Soter, Antigonus and Eurydice, the ambitious wife of king Philip Arrhidaeus, and declared war upon the Regency. Polyperchon was allied with Eumenes and Olympias.

Although Polyperchon was successful at first, taking control of the Greek cities, his fleet was destroyed by Antigonus in 318 BC. When, after the battle, Cassander assumed full control of Macedon, Polyperchon was forced to flee to Epirus, followed by Roxana and the young Alexander. A few months later, Olympias was able to persuade her relative Aeacides of Epirus to invade Macedon with Polyperchon. When Olympias took the field, Eurydice's army refused to fight against the mother of Alexander and defected to Olympias, after which Polypercheron and Aeacides retook Macedon. Philip and Eurydice were captured and executed on December 25, 317 BC, leaving Alexander IV king, and Olympias in effective control, as she was his regent.

Cassander returned in the following year (316 BC), conquering Macedon once again. Olympias was immediately executed, while the king and his mother were taken prisoner and held in the citadel of Amphipolis under the supervision of Glaucias. When the general peace between Cassander, Antigonus, Ptolemy, and Lysimachus put an end to the Third Diadoch War in 311 BC, the peace treaty recognized Alexander IV's rights and explicitly stated that when he came of age he would succeed Cassander as ruler.

Following the treaty, defenders of the Argead dynasty began to declare that Alexander IV should now exercise full power and that a regent was no longer needed. Cassander's response was definitive: to secure his rule, in 309 BC he commanded Glaucias to secretly assassinate the 13-year old Alexander IV and his mother. The orders were carried out, and they were both poisoned.

*Smith, William (editor); Dictionary of Greek and Roman Biography and Mythology, "Alexander IV", Boston, (1867)

The tragic young monarch appears as a character in Funeral Games, a historical novel by Mary Renault.

*Wiki Classical Dictionary: Alexander IV