Tiberius Claudius Caesar Britannicus (c. 12 February AD 41 – 11 February AD 55), usually called Britannicus, was the son of Roman emperorClaudius and his third wife Valeria Messalina. For a time he was considered his father's heir, but that changed after his mother's downfall in 48, when it was revealed she had a bigamous marriage without Claudius' knowledge. The next year, his father married Agrippina the Younger, Claudius' fourth and final marriage. Their marriage was followed by the adoption of Agrippina's son, Lucius Domitius, whose name became Nero as a result. His step-brother would later be married to his sister Octavia, and soon eclipsed him as Claudius' heir. Following his father's death in October 54, Nero became emperor. The sudden death of Britannicus shortly before his fourteenth birthday is reported by all extant sources as a poisoning on Nero's orders—as Claudius' natural son, he represented a threat to Nero's claim to the throne.
Britannicus' name at birth was Tiberius Claudius Germanicus. The agnomen, his first surname Germanicus, was first awarded to his paternal grandfather Drusus the Elder after his death in 9 BC to commemorate his victories over the Germanic tribes. Accordingly, Drusus' sons (Claudius and Germanicus) inherited the name and passed it to their sons as well. Britannicus was given to his father in AD 43 following his conquest of Britain. Claudius never used it himself and gave the name to his son instead, and his full name became: Tiberius Claudius Caesar Britannicus. He came to be known by his new name which seems to have replaced Germanicus altogether.