Togodumnus (d. AD 43) was a historical king of the British Catuvellauni tribe at the time of the Roman conquest. He can probably be identified with the legendary British king Guiderius.
He is usually thought to have led the fight against the Romans alongside his brother, but to have been killed early in the campaign. However, some authorities now argue that he sided with the Romans and is one and the same person as the client-king Tiberius Claudius Cogidubnus, whose original name may have been Togidubnus or Togodumnus.
Togodumnus is known only from Cassius Dio's Roman History, according to which he was a son of Cunobelinus. He probably succeeded his father to the kingship of the Catuvellauni, who were the dominant kingdom in the south-east of Britain at this time. Their territory took in the lands of several other nations, including their neighbours the Trinovantes, and possibly the Dobunni further west.
He had two notable brothers, Adminius and Caratacus. In Cunobelinus's later days Adminius gained control of the Cantiaci in Kent, but was driven from Britain in 40 AD, seeking refuge with the Roman emperor Caligula. Caligula planned an invasion of Britain in response, but called it off at the last minute.