Tiberius Julius Caesar Nero, known as Tiberius Gemellus, was the son of Drusus and Livilla, the grandson of the Emperor Tiberius, and the cousin of the Emperor Caligula. Gemellus is a nickname meaning "the twin". His twin brother, Germanicus Gemellus, died as a young child in AD 23. His father and older cousins died, and are suspected by contemporary sources as having been systematically eliminated by the powerful praetorian prefect Sejanus. Their removal allowed Gemellus and Caligula to be named joint-heirs by Tiberius in 35, a decision that ultimately resulted in Caligula assuming power and having Gemellus killed in late 37 or early 38.

Drusus Julius Caesar, also called Drusus the Younger, was the son of Emperor Tiberius, and heir to the Roman Empire following the death of his adoptive brother Germanicus in AD 19.