Caratacus (also spelled Caractacus) was a historical British chieftain of the Catuvellauni tribe, who led the British resistance to the Roman conquest. He may correspond with the legendary Welsh character Caradog (also written Caradoc, Caradawg) and the legendary British king Arvirargus.

Probably the youngest son of king Cunobelinus (William Shakespeare's Cymbeline), Caratacus appears to have been the protegé of his uncle Epaticcus, who expanded Catuvellaunian power westwards into the territory of the Atrebates. After Epaticcus died ca. 35 AD, and the Atrebates, under Verica, regained some of their territory, Caratacus completed the conquest. Verica, in a last attempt to secure power, appealed to the Roman Empire for help. This plea was the excuse emperor Claudius used to invade Britain. Along with his brother Togodumnus, Caratacus led the defence of the country, but they were defeated: Togodumnus was killed in the Battle of Medway and Caratacus was forced to flee.

Afterwards, when his tribesmen accepted the Roman occupation, Caratacus continued to struggle. He fought actively against governor Aulus Plautius both in southern England and in Wales, where he fled to after the Catuvellauni surrendered. In Welsh lands, he organised the resistance of the Silures and Ordovices tribes against Roman presence. Caratacus gave plenty of trouble to the successor of Plautius, governor Publius Ostorius Scapula, who had great difficulty in dealing with his uprisings. Finally, in 51 CE, Scapula managed to defeat Caratacus in the Battle of Caer Caradock and Caratacus was forced to flee once more, this time to the North. Caratacus sought asylum in the Brigantes lands of queen Cartimandua, but she betrayed him and delivered him to the Romans as a proof of her allegiance.

After his capture, Caratacus was sent to Rome as a war prize, presumably to be killed after a triumphal parade. Although a captive, he was allowed to speak to the Roman senate. Tacitus records a version of his speech, in which he says that his stubborn resistance made Rome's glory in defeating him all the greater, and adds "If you want to rule the world, does it follow that everyone else welcomes enslavement?" He made such an impression that he was pardoned and allowed to live in peace inside Rome. After his liberation, according to Dio Cassius, Caratacus was so impressed by the city of Rome that he said "Why do you, who possess so many palaces, covet our poor tents?"

His fame survived for several centuries. A genealogy of an otherwise unknown British king in the Historia Britonum traced his ancestry to Caratacus. Lot, King or king of Lothian, Orkney, and Norway in Arthurian legend was reportedly his descendant.