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 the narrative of Ctesias, to give it in a much-abbreviated form, is something as follows. After he had slain Artagerses, Cyrus rode against the king himself, and the king against him, both without a word. But Ariaeus, the friend of Cyrus, was beforehand in hurling his spear at the king, though he did not wound him. And the king, casting his spear at Cyrus, did not hit him, but struck and killed Satiphernes, a trusted friend of Cyrus and a man of noble birth. But Cyrus threw his spear at the king and wounded him in the breast through the cuirass, so that the weapon sank in two fingers deep, and the king fell from his horse with the blow.
Amid the ensuing confusion and flight of his immediate followers, the king rose to his feet, and with a few companions (among whom also was Ctesias), took possession of a certain hill near by and remained there quietly; but Cyrus, enveloped by his enemies, was borne on a long distance by his spirited horse, and since it was now dark, his enemies did not recognize him and his friends could not find him. But lifted up by his victory, and full of impetuosity and confidence, he rode on through his foes, crying out, "Clear the way, ye beggars!"
Thus he cried out many times, in Persian, and they cleared the way, and made him their obeisance. But the tiaranote[The royal turban.] of Cyrus fell from his head, and a young Persian, Mithridates by name, running to his side, smote him with his spear in the temple, near the eye, not knowing who he was. Much blood gushed from the wound, and Cyrus, stunned and giddy, fell to the ground. His horse escaped and wandered about the field, but the horse's saddle-cloth, which had slipped off, was captured by the attendant of the man who had struck Cyrus, and it was soaked with blood. Then, as Cyrus was slowly and with difficulty recovering from the blow, a few eunuchs who were at hand tried to put him upon another horse and bring him to a place of safety. But since he was unable to ride and desired to go on his own feet, they supported him and led him along. His head was heavy and he reeled to and fro, but he thought he was victorious because he heard the fugitives saluting Cyrus as king and begging him to spare them.
Meanwhile some Caunians - low and poverty-stricken men who followed the king's army to do menial service - chanced to join the party about Cyrus, supposing them to be friends. But when at last they perceived that the tunics over their breastplates were of a purple color, whereas all the king's people wore white ones, they knew that they were enemies. Accordingly, one of them, not knowing who Cyrus was, ventured to smite him from behind with his spear. The vein in the ham of Cyrus was ruptured and he fell, and at the same time struck his wounded temple against a stone, and so died. Such is the story of Ctesias, in which, as with a blunt sword, he is long in killing Cyrus, but kills him at last.
 When Cyrus was now dead, Artasyras, the king's eye, chanced to pass by on horseback, and recognizing the eunuchs as they lamented, he asked the trustiest of them, "Who is this man, Pariscas, by whom thou sittest mourning?" And Pariscas answered: "O Artasyras, dost thou not see Cyrus dead?"
Astonished at this, then, Artasyras bade the eunuch be of good courage and guard the dead body, but he himself went in hot haste to Artaxerxes (who had already given up his cause for lost, and besides was physically in a wretched plight from thirst and from his wound), and joyfully told him that with his own eyes he had seen Cyrus dead. At first the king promptly set out to go in person to the place, and ordered Artasyras to conduct him thither; but since there was much talk about the Greeks, and it was feared that they were pursuing and conquering and making themselves masters everywhere, he decided to send a larger company to see where Cyrus lay. So thirty men were sent, with torches.
Meanwhile, since the king was almost dead with thirst, Satibarzanes the eunuch ran about in quest of a drink for him; for the place had no water, and the camp was far away. At last, then, he came upon one of those low Caunians, who had vile and polluted water in a wretched skin, about two quarts in all: this he took, brought it to the king, and gave it to him. After the king had drunk it all off, the eunuch asked him if he was not altogether disgusted with the drink. But the king swore by the gods that he had never drunk wine, or the lightest and purest water, with so much pleasure. "Therefore," said the king, "if I should be unable to find and reward the man who gave thee this drink, I pray the gods to make him rich and happy."
 And now the thirty messengers came riding up with joy and exultation in their faces, announcing to the king his unexpected good fortune. Presently, too, he was encouraged by the number of men who flocked back to him and formed in battle array, and so he came down from the hill under the light of many torches. And after he had halted at the dead body of Cyrus, and its right hand and head had been cut off (in accordance with a law of the Persians), he ordered the head to be brought to him; and grasping it by the hair, which was long and bushy, he showed it to those who were still wavering and disposed to fly. These were amazed, and made obeisance to the king, so that very soon seventy thousand men were about him and marched back with him to their camp.
He had marched out to the battle, as Ctesias says, with four hundred thousand men. But Deinon and Xenophon say that the army which fought under him was much larger. As to the number of his dead, Ctesias says that it was reported to Artaxerxes as nine thousand, but that he himself thought the slain no fewer than twenty thousand. This matter, then, is in dispute. But it is certainly a glaring falsehood on the part of Ctesias to say that he was sent to the Greeks along with Phalinus the Zacynthian and certain others. For Xenophon knew that Ctesias was in attendance upon the king, since he makes mention of him and had evidently read his works; if, then, Ctesias had come to the Greeks and served as an interpreter in so momentous a colloquy, Xenophon would not have left him nameless and named only Phalinus the Zacynthian. The truth is that Ctesias, being prodigiously ambitious, as it would seem, and none the less partial to Sparta and to Clearchus, always allows considerable space in his narrative for himself, and there he will say many fine things about Clearchus and Sparta.
 After the battle, the king sent the largest and most beautiful gifts to the son of that Artagerses who fell at the hands of Cyrus; he also gave generous rewards to Ctesias and others, and when he had found out the Caunian who had given him the skin of water, he raised him from obscurity and poverty to honor and wealth.
There was much watchful care also in his punishment of those who had gone wrong. For example, in the case of Arbaces, a Mede, who had run away to Cyrus during the battle, and, when Cyrus fell, had changed back again, the king pronounced him guilty, not of treachery, nor even of malice, but of cowardice and weakness, and ordered him to take a naked harlot astride his neck and carry her about in the market-place for a whole day.
And in the case of another man, who, besides going over to the enemy, had lyingly boasted that he had slain two of them, the king ordered that his tongue should be pierced with three needles.
Moreover, believing, and wishing all men to think, say, that he had killed Cyrus with his own hand, he sent gifts to Mithridates, the one who first hit Cyrus, and ordered the bearers of the gifts to say: "This is thy reward from the king because thou didst find and bring to him the trappings of the horse of Cyrus."
Again, when the Carian, from whom Cyrus received the blow in the ham which brought him down, asked that he all should receive a gift, the king ordered its bearers to say: "The king gives thee these things as a second prize for good tidings; for Artasyras came first, and after him thou didst come, with tidings of the death of Cyrus."
Now, Mithridates went away without a word, although he was vexed; but the wretched Carian, in his folly, gave way to a common feeling. That is, he was corrupted, it would seem, by the good things which he had, and led by them to aspire at once to things beyond his reach, so that he would not deign to take the gifts as a reward for good tidings, but was indignant, calling men to witness and crying in loud tones that it was he himself, and no one else, who had killed Cyrus, and that he was unjustly robbed of his glory. When the king heard of this, he was vehemently angry and gave orders that the man should be beheaded. Whereupon the king's mother, who was present, said to him: "O King, do not let this accursed Carian off so easily, but leave him to me, and he shall receive the fitting reward for his daring words." So the king consigned the man to Parysatis, who ordered the executioners to take him and rack him on the wheel for ten days, then to gouge out his eyes, and finally to drop molten brass into his ears until he died.
 Mithridates also came to a miserable end a little while after, of that same folly. For being invited to a banquet at which eunuchs of the king and of the queen-mother were present, he came decked out with raiment and gold which he had received from the king. And when the company were at their cups, the chief eunuch of Parysatis said to him: "Mithridates, how beautiful this raiment is which the king gave thee, and how beautiful the collars and bracelets! Costly, too, is thy scimitar. Verily the king has made thee happy in the admiring eyes of all men."
Then Mithridates, now flushed with wine, replied: "Sparamizes, what do these things amount to? Surely my services to the king on that day were worthy of greater and more beautiful gifts."
Here Sparamizes smiled at him and said: "There's no grudging them to thee, Mithridates; but since, according to the Greek maxim, there is truth in wine, what great or brilliant exploit was it, my good fellow, to find a horse's trappings that had slipped off, and bring them to the king?"
In saying this, Sparamizes was not ignorant of the truth, but he wished to unveil Mithridates to the company, and therefore slyly stirred up his vanity when wine had made him talkative and robbed him of self-control. Accordingly, Mithridates threw away constraint and said: "Ye may talk as ye please about horse-trappings and such nonsense; but I declare to you explicitly that Cyrus was slain by this hand of mine; for I did not, like Artagerses, make a futile and an idle cast of spear, but I narrowly missed his eye, struck him in the temple, pierced it, and brought the man down; and it was of that wound that he died."
The rest of the company, who already saw the end of Mithridates and his hapless fate, bowed their faces towards the ground; and their host said: "My good Mithridates, let us eat and drink now, revering the good genius of the king, and let us waive discourse that is too weighty for us."