Brutus of Troy, also of Britain (Welsh: Bryttys), was the legendary founding king of Britain and great grandson of Aeneas, according to Geoffrey of Monmouth. Exiled from Italy for the accidental killing of his natural father Silvius, Brutus liberated a group of Trojans living in slavery in Greece and led them forth, received a vision during this wandering that he would found a kingdom in a land inhabited by giants, then after numerous battles in the region of the city of Tours in Gaul, he settled in Britain with the aid of his fellow Trojan Corineus, where they slew the giants living in that island. He is said to have founded the city Troia Nova, later named London. The Celtic tribe that dwelt in the area of London was called the Trinovantes, and one early name of the city named it after them. He created a code of laws for his people before his death. He reigned 23 years. By Ignoge he had three sons — Locrinus, Kamber, and Albanactus — whom on Brutus's death divided the island between them.

Geoffrey fixes the time of his death with the statement that Eli was priest in Judea and the Ark of the Covenant was captured by the Philistines, the sons of Hector reigned in Troy, and Aeneas Silvius was ruling Alba Longa in Italy.

Although the Historia Britonum, from which Geoffrey drew the core of this story, claims Britain was named after Brutus, this personage has no basis in actual fact, and is generally considered a medieval fiction created to provide a distinguished genealogy for one or more Welsh royal families. The Historia Britonum not only describes Brutus as a descendent of Troy but also places him in the Trojan genealogy, which he probably created himself to relate Troy to the Christian God.

Brutus became part of the Matter of Britain, a pseudo-historical account of the events of that island, which was widely accepted as historical fact until the seventeenth and eighteenth centuries, when reliable historical records and inscriptions were available and studied by scholars who gradually disproved much of it — but is still occasionally cited in popular or ceremonial accounts in contemporary England.