Bagoas (or Βαγώας, Greek transcription of Old Persian Bagoi; died 336 BC) was a eunuch who became the vizier (Chief Minister) to Artaxerxes III. In this role, he allied himself with the Rhodian mercenary general Mentor, and with his help succeeded in once again making Egypt a province of the Persian Empire (probably from 342 BC). Mentor became general of the maritime provinces, suppressed the rebels in Egypt and sent Greek mercenaries to the king, while Bagoas administered the satrapies and gained such power that he was the real master of the Persian Empire towards the end of Artaxerxes III's reign (Diod. xvi. 50; cf. Didymus, Comm. in Demosth. Phil. vi. 5).
Artaxerxes IV Arses was the youngest son of King Artaxerxes III and Atossa and was not expected to succeed to the throne of Persia. His unexpected rise to the throne came in 338 BC as a result of the murder of his father and most of his family by Bagoas, when the vizier fell our of favour with Artaxerxes III. Bagoas sought to remain in office by replacing Artaxerxes with his son Arses (Artaxerxes IV), whom he thought easier to control. Arses remained little more than a puppet-king during the two years of his reign while Bagoas acted as the power behind the throne. Eventually, disgruntled by this state of affairs and possibly influenced by the nobles of the Royal Court, who generally held Bagoas in contempt, Arses started planning Bagoas' murder. However, Bagoas again acted first in order to protect himself and managed to poison and kill Arses. Bagoas then raised a cousin of Arses to the throne as King Darius III of Persia.
When Darius attempted to become independent of the powerful vizier, Bagoas tried to poison him too; but Darius was warned and forced Bagoas to drink the poison himself (Diod. xvii. 5; Johann. Antioch, p. 38, 39 ed. Müller; Arrian ii. 14. 5; Curt. vi. 4. 10).
It was said that Bagoas became very wealthy by confiscating the sacred writings of the Egyptian temples and giving them back to the priests for large bribes (Diod. XVI. 51). When the high priest of Jerusalem murdered his brother Johannes in the temple, Bagoas (who had supported Johannes) put a new tax on the Jews and entered the temple, saying that he was purer than the murderer who performed the priestly office (Joseph. Ant. xi. 7.1).
A later story, that Bagoas was an Egyptian and killed Artaxerxes III because he had killed the sacred Apis (Aelian, Var. Hist. vi. 8), is without historical basis.
Bagoas' house in Susa, with rich treasures, was presented by Alexander to Parmenion (Plut. Alex. 39); his gardens in Babylon, with the best species of palms, are mentioned by Theophrastus (Hist. Plant, ii. 6; Plin. Nat. Hist. xiii. 41).
Plutarch reports an angry letter from Alexander to Darius, naming Bagoas as one of the persons that organized the murder of his father, Philip II.