Wikipedia
Cassivellaunus
Cassivellaunus was a historical British tribal chief who led the defence against Julius Caesar's second expedition to Britain in 54 BC. He led an alliance of tribes against Roman forces, but eventually surrendered after his location was revealed to Julius Caesar by defeated Britons.
Cassivellaunus made an impact on the British consciousness. He appears in British legend as Cassibelanus, one of Geoffrey of Monmouth's kings of Britain, and in the Mabinogion, the Brut y Brenhinedd and the Welsh Triads as Caswallawn, son of Beli Mawr. His name in Common Brittonic, *Cassiuellaunos, comes from Proto-Celtic *kassi- "passion, love, hate" (alternately, "long hair", or "bronze") + *uelna-mon- "leader, sovereign".