When he was still very small, Claudius would often take him in his arms and commend him to the assembled soldiers, and to the people at the games, holding him in his lap or in his outstretched hands, and he would wish him happy auspices, joined by the applauding throng.While Britannicus was just a boy, Claudius adopted Nero, his grandnephew, to assure the succession in case Claudius should die before Britannicus reached adulthood. It was said that Claudius had every intention of making Britannicus his heir "that the Roman people may at last have a genuine Caesar" according to Suetonius. However, Claudius died in AD 53, poisoned it was said by Agrippina the Younger, his third wife and the mother of Nero. Agrippina and her allies in the senate were able gain approval for Nero to rule and he was acclaimed emperor, though some sources say that Claudius meant for the boys to rule jointly or even for Britannicus to rule alone. In any event, Agrippina made sure that Britannicus and the other natural children of Claudius remained isolated politically.
With a few months, Nero and Agrippina felt secure enough to deal with Britannicus permanently. Like his father before him, he was poisoned and it is said that he breathed his last in the presence of his friend Titus--later Roman emperor in his own right.
A scene from the end of the I, Claudius TV series depicts the relationship between Claudius and his son Britannicus and offers a possible explanation for Claudius's apparent favoring of Nero at the end of his life:
Given the monstrous nature of Nero and his reign, it is interesting to speculate how Roman and Christian history may have been different if Britannicus had ruled instead. For a more detailed biography of Britannicus, see the De Imperatoribus Romanis site.