Plutarch of Chaeronea (46-c.122): influential Greek philosopher and author, well known for his biographies and his moral treatises. His biography is here; his Life of Artaxerxes is the only biography not dedicated to a Greek or a Roman, but describes the life of the Persian king Artaxerxes II Mnemon (r. 404-358).
Plutarch's Life of Artaxerxes is a remarkable treatise, because the author has inserted much confused and disjointed information, has included unusually lengthy quotations (from Ctesias), and is - Plutarch always being a Greek in the first place - uncharacteristically kind towards "the barbarian". In other words, it is possibly not written by Plutarch.
The author uses Xenophon and Deinon as his sources, but especially the notoriously unreliable Ctesias of Cnidus, whom he criticizes. Another authority is Heracleides of Cyme.
The translation offered here was made by Bernadotte Perrin; it was originally put online (with all original notes from the Loeb edition) by Bill Thayer on LacusCurtius.
 But Artaxerxes, being now advanced in years, perceived that his sons were forming rival parties among his friends and chief men with reference to the royal succession. For the conservatives thought it right that, as he himself had received the royal power by virtue of seniority, in like manner he should leave it to Dareius. But his youngest son, Ochus, who was of an impetuous and violent disposition, not only had many adherents among the courtiers, but hoped for most success in winning over his father through the aid of Atossa. For he sought to gain Atossa's favor by promising that she should be his wife and share the throne with him after the death of his father. And there was a report that even while his father was alive Ochus had secret relations with Atossa.
But Artaxerxes was ignorant of this; and wishing to shatter at once the hopes of Ochus, that he might not venture upon the same course as Cyrus and so involve the kingdom anew in wars and contests, he proclaimed Dareius, then fifty years of age, his successor to the throne, and gave him permission to wear the upright kitanis, as the tiara was called.
Now, there was a custom among the Persians that the one appointed to the royal succession should ask a boon, and that the one who appointed him should give whatever was asked, if it was within his power. Accordingly, Dareius asked for Aspasia, who had been the special favorite of Cyrus, and was then a concubine of the king. She was a native of Phocaea, in Ionia, born of free parents, and fittingly educated. Once when Cyrus was at supper she was led in to him along with other women. The rest of the women took the seats given them, and when Cyrus proceeded to sport and dally and jest with them, showed no displeasure at his friendly advances. But Aspasia stood by her couch in silence, and would not obey when Cyrus called her; and when his chamberlains would have her led to him, she said: "Verily, whosoever lays his hands upon me shall rue the day."
The guests therefore thought her a graceless and rude creature. But Cyrus was delighted, and laughed, and said to the man who had brought the women: "Dost thou not see at once that this is the only free and unperverted woman thou hast brought me?" From this time on he was devoted to her, and loved her above all women, and called her The Wise. She was taken prisoner when Cyrus fell in the battle at Cunaxa and his camp was plundered.
 This was the woman for whom Dareius asked, and he gave offence thereby to his father; for the Barbarian folk are terribly jealous in all that pertains to the pleasures of love, so that it is death for a man, not only to come up and touch one of the royal concubines, but even in journeying to go along past the waggons on which they are conveyed. And yet there was Atossa, whom the king passionately loved and had made his wife contrary to the law, and he kept three hundred and sixty concubines also, who were of surpassing beauty.
However, since he had been asked for Aspasia, he said that she was a free woman, and bade his son take her if she was willing, but to constrain her against her wishes. So Aspasia was summoned, and contrary to the hopes of the king, chose Dareius. And the king gave her to Dareius under constraint of the custom that prevailed, but a little while after he had given her, he took her away again. That is, he appointed her a priestess of the Artemis of Ecbatana, who bears the name of Anaitis, in order that she might remain chaste for the rest of her life, thinking that in this way he would inflict a punishment upon his son which was not grievous, but actually quite within bounds and tinctured with pleasantry. The resentment of Dareius, however, knew no bounds, either because he was deeply stirred by his passion for Aspasia, or because he thought that he had been insulted and mocked by his father.
And now Teribazus, who became aware of the prince's feelings, sought to embitter him still more, finding in his grievance a counterpart of his own, which was as follows. The king had several daughters, and promised to give Apama in marriage to Pharnabazus, Rhodogyne to Orontes, and Amestris to Teribazus. He kept his promise to the other two, but broke his word to Teribazus and married Amestris himself, betrothing in her stead to Teribazus his youngest daughter, Atossa. But soon he fell enamoured of Atossa also and married her, as has been said, and then Teribazus became a downright foe to him. Teribazus was at no time of a stable disposition, but uneven and precipitate. And so, when he would be at one time in highest favour, and at another would find himself in disgrace and spurned aside, he could not bear either change of fortune with equanimity, but if he was held in honour his vanity made him offensive, and when he fell from favour he was not humble or quiet, but harsh and ferocious.
 Accordingly, it was adding fire to fire when Teribazus attached himself to the young prince and was forever telling him that the tiara standing upright on the head was of no use to those who did not seek by their own efforts to stand upright in affairs of state, and that he was very foolish if, when his brother was insinuating himself into affairs of state by way of the harem, and his father was of a nature so fickle and insecure, he could suppose that the succession to the throne was securely his. Surely he whom regard for a Greek courtesan had led to violate the inviolable custom of the Persians, could not be trusted to abide by his agreements in the most important matters. Moreover, he said it was not the same thing for Ochus not to get the kingdom and for Dareius to be deprived of it; for no one would hinder Ochus from living happily in private station, but Dareius had been declared king, and must needs be king or not live at all.
Now, perhaps it is generally true, as Sophocles says, that
"Swiftly doth persuasion upon evil conduct make its way"
for smooth and downward sloping is the passage to what a man desires, and most men desire the bad through inexperience and ignorance of the good. However, it was the greatness of the empire and the fear which Dareius felt towards Ochus that paved the way for Teribazus although, since Aspasia had been taken away, the Cyprus-born goddess of lovenote[Aphrodite.] was not altogether without influence in the case.
 Such, then, was the end of the conspiracy. And now Ochus was sanguine in the hopes with which Atossa inspired him, but he was still afraid of Ariaspes, the only legitimate son of the king remaining, and also of Arsames among the illegitimate sons. For Ariaspes, not because he was older than Ochus, but because he was mild and straightforward and humane, was deemed by the Persians worthy to be their king; Arsames, however, was thought to have wisdom, and the fact that he was especially dear to his father was not unknown to Ochus.
Accordingly, he plotted against the lives of both, and being at once wily and bloody-minded, he brought the cruelty of his nature into play against Arsames, but his villainy and craft against Ariaspes. For he secretly sent to Ariaspes eunuchs and friends of the king, who constantly brought him word of sundry threatening and terrifying utterances implying that his father had determined to put him to a cruel and shameful death.
Since they pretended that these daily reports of theirs were secrets of state, and declared, now that the king was delaying in the matter, and now that he was on the point of acting, they so terrified the prince, and filled his mind with so great trepidation, confusion, and despair, that he drank a deadly poison which he had prepared, and thus rid himself of life. When the king was informed of the manner of his death, he bewailed his son. He also suspected what had caused his death, but being unable by reason of his age to search out and convict the guilty one, he was still more well-affectioned towards Arsames, and clearly made him his chief support and confidant. Wherefore Ochus would not postpone his design, but set Arpates, a son of Teribazus, to the task and by his hand slew the prince.
Now Artaxerxes, by reason of his age, was already hovering between life and death; and when the sad fate of Arsames came to his ears, he could not hold out even a little while, but straightway expired of grief and despair. He had lived ninety-four years, and had been king sixty-two, and had the reputation of being gentle and fond of his subjects; though this was chiefly due to his son Ochus, who surpassed all men in cruelty and blood-guiltiness.