Androgeus was a legendary Duke of Trinovantum and Kent as accounted by Geoffrey of Monmouth. He was the eldest son of King Lud and the rightful heir to the British throne. Due to his youth, however, his uncle Cassivelaunus ruled as regent until the nobles crowned him king of the Britons.

Androgeus was given the Duchy of Kent and Trinovantum by his uncle following the death of Lud. As he grew older, he became a trusted advisor to the king and helped in the first two attacks by the Romans who were under the leadership of Julius Caesar.

At the celebration following the second successful battle against the Romans, a nephew of Androgeus killed a nephew of the king. Because Androgeus would not permit the king to kill his own nephew, Cassivelaunus ravaged his lands. Unable to defend himself, he sought the help of Caesar, who was on a nearby island brooding over his loss. After giving him hostages, including his own son Scaeva, to Caesar as proof he is willing to aid him in Britain, Caesar invaded and Androgeus helped him take over London in the night. When the Britons counterattacked, Caesar gained the upper hand and forced them onto a hill for two days. Cassivelaunus finally pleaded with Androgeus to surrender Britain to Caesar. He submitted and discussed terms with Caesar. The island became a dominion of Rome and Caesar wintered there then left for Gaul in the spring.

Androgeus departed with Caesar that spring and never returned. Because of that, his brother Tenvantius became king following Cassivelaunus's death. Androgeus's son, Scaeva, apparently went with his father, was dead, or not strong enough to claim the throne of Britain in his stead.