The son of Tarquinius Superbus.
While fighting the neighboring town of Gabii, Tarquinius Superbus encountered difficulties taking the town. He therefore sent his youngest son Sextus to the town, acting as if he was forced to flee from his father. Since he had intimate knowledge of Rome and her king, the Gabii gladly received him. Eventually, Sextus worked his way up to be general of their army. He won many minor battles against the Romans, and soon was the most powerful man in the city. Sextus then set about killing every leader of the Gabii, and then handed the town to Tarquinius Superbus without a fight.
Later, while besieging the town of Ardea, he and his cousin Collatinus got into an argument about whose wife was better. Someone got the idea to simply go to each man's house and see what their wives were doing. The men were all drunk, and this sounded like a good idea. In Rome, they found Sextus' wife at a party. Collatinus' beautiful wife Lucretia was busy at home with housework. Collatinus had clearly won the argument, and Sextus became enamored with Lucretia. The next night, Sextus returned to Rome and raped Lucretia.
It was this incident that sparked the overthrow of Tarquinius Superbus and the establishment of the Republic. When his father was expelled, Sextus foolishly returned to Gabii, which he had betrayed into Roman hands. The people of Gabii had not forgotten, and he was murdered after entering the town.
Livy. Ab Urbe Condita.