o-ni'-as (Onias): There were 3 high priests of the name of Onias, and a 4th Onias who did not become a high priest but was known as the builder of the temple of Leontopolis (Josephus, Ant, XIII, iii, 1-3). Only two persons of the name are mentioned in the Apocrypha--Onias I and Onias III.
(1) Onias I, according to Josephus (Ant., XI, viii, 7), the son of Jaddua and father of Simon the Just (ibid., XII, ii, 5; Sirach 50), and, according to 1 Macc 12:7,20, a contemporary of Areus (Arius), king of Sparta, who reigned 309-265 BC (Diod. xx.29). This Onias was the recipient of a friendly letter from Areus of Sparta (1 Macc 12:7; see manuscripts readings here, and 12:20). Josephus (Ant., XII, iv, 10) represents this letter as written to Onias III, which is an error, for only two Areuses are known, and Areus II reigned about 255 BC and died a child of 8 years (Paus. iii.6,6). The letter--if genuine--exists in two copies (Josephus, Ant, XII, iv, 10, and 1 Macc 12:20 ff) (see Schurer, History of the Jewish People, 4th edition, I, 182 and 237).
(2) Onias III, son of Simon II (Josephus, Ant, XII, iv, 10), whom he succeeded, and a contemporary of Seleucus IV and Antiochus Epiphanes (2 Macc 3:1; 4:7) and father of Onias IV. He was known for his godliness and zeal for the law, yet was on such friendly terms with the Seleucids that Seleucus IV Philopator defrayed the cost of the "services of the sacrifices." He quarreled with Simon the Benjamite, guardian of the temple, about the market buildings (Greek aedileship). Being unable to get the better of Onias and thirsting for revenge, Simon went to Apollonius, governor of Coele-Syria and Phoenicia, and informed him of the "untold sums of money," lodged in the treasury of the temple. The governor told the king, and Seleucus dispatched his chancellor, Heliodorus, to remove the money. Onias remonstrated in vain, pleading for the "deposits of widows and orphans." Heliodorus persisted in the object of his mission. The high priest and the people were in the greatest distress. But when Heliodorus had already entered the temple, "the Sovereign of spirits, and of all authority caused a great apparition," a horse with a terrible rider accompanied by two strong and beautiful young men who scourged and wounded Heliodorus. At the intercession of Onias, his life was spared. Heliodorus advised the king to send on the same errand any enemy or conspirator whom he wished punished. Simon then slandered Onias, and the jealousy having caused bloodshed between their followers, Onias decided to repair in person to the king to intercede for his country. Apparently before a decision was given, Seleucus was assassinated and Epiphanes succeeded (175 BC). Jason, the brother of Onias, having offered the new king larger revenue, secured the priesthood, which he held until he himself was similarly supplanted by Menelaus, Simon's brother (2 Macc 4:23; Josephus, Ant, XII, v, 1, says Jason's brother). Menelaus, having stolen golden vessels belonging to the temple to meet his promises made to the king, was sharply reproved by Onias. Menelaus took revenge by persuading Andronicus, the king's deputy, to entice Onias by false promises of friendship from his sanctuary at Daphne and treacherously slay him--an act which caused indignation among both the Jews and the Greeks (2 Macc 4:34 ff). Josephus (Ant., XII, v, 1) says that "on the death of Onias the high priest, Antiochus gave the high-priesthood to his brother Jesus (Jason)," but the account of 2 Macc given above is the more probable. Some see in Da 9:26; 11:22 reference to Onias III (Schurer, 4th edition, I, 194 ff; III, 144).