No one we know of has ever exacted a more total retribution for a wrong done to him than Hermotimus. He was taken prisoner in a war, put for sale, and bought by a man from Chios called Panionius. Now, Panionius made a living in the most atrocious way imaginable. What he used to do was acquire good-looking boys, castrate them, and take them to Sardis and Epheseus, where he would offer them for sale at very high prices; in foreign countries eunuchs command higher prices than whole men on account of their complete reliability. One of Panionius' victims -- one among a great many, because this was they way he made a living -- was Hermotimus. In fact, however, Hermotimus' luck was not all bad: he was sent from Sardis to Xerxes' court as one of a number of gifts, and eventually became the king's most valued eunuch.
Now, when Xerxes was in Sardis, in the course of setting out with his army against Athens, Hermotimus went down on some business or other to the part of Mysia called Atarneus, where people from Chios live, and he met Panionius there. He entered into a long, friendly conversation with him, first listing all the benefits that had come his way thanks to Panionius, and then offering to do as much good to him in return; all he had to do, he said, was move his family to Atarneus and live there. Panionius gladly accepted Hermotimus' offer and moved his wife and children there.
So when Hermotimus had Panionius and his whole family where he wanted, he said, "Panionius, there is no one the the world who makes a living in as foul a way as you do. What harm did I or any of my family do to you or any of yours? Why did you make me a nothing instead of a man? You expected the gods not to notice what you used to do in those days, but the law they follow is one of justice, and for your crimes they have delivered you into my hands. As a result, then, you should have no grounds for complaint about the payment I am going to extract from you."
When he had finished this rebuke, he had Panionius's sons brought into the room and proceeded to force him to castrate all four of them. The deed was done, under compulsion, and afterwards Hermotimus forced the sons to castrate their father. And that is how vengeance and Hermotimus caught up with Panionius.
from The Histories, by Herodotus