Tiberius Drusus Julius Caesar, also referred to as Drusus II (13 BC-July 1, 23 AD) was the only son of Tiberius and Tiberius's first wife, Vipsania Agrippina.

Despite his violent temper, Drusus showed promise with both military and politics. In 13 AD he was made a permanent member of the Senate committee Augustus had founded to draw up the Senate's daily business. However, because Drusus was only related to the Claudian side of the family, rather than both the Julians and Claudians, Augustus forced Tiberius to adopt Germanicus as his son and heir, removing Drusus from the succession. In 14, after the death of Augustus, Drusus suppressed a mutiny in Pannonia. In 15 he became a consul. He was also governor of Illyricum from 17 to 20. In 21 he was consul again, and was tribune in 22.

Drusus married his cousin Livilla circa 4 AD. Their daughter Livia Julia was born shortly after. They had twin sons Tiberius Gemellus and Germanicus Gemellus in 19. That same year, Germanicus died, making Drusus the new heir; Germanicus' wife Agrippina suspected Tiberius of having killed him to allow Drusus to become his heir, but this is unlikely.

Before the birth of the twins, Livilla had already been in a relationship with Sejanus, Tiberius' Praetorian Prefect. Sejanus convinced Livilla to poison her husband in a plot to eventually overthrow Tiberius. Drusus was very bitter towards Sejanus; he supposedly once punched Sejanus in the face. Drusus died in the year 23. Sejanus then tried to marry Livilla but Tiberius forbade it. The truth about Drusus' death would not be revealed until 31 by Sejanus' wife: Sejanus had poisoned him, but Tiberius refused to believe this, either in 23 or in 31. Livilla would be excuted shortly after this revelation.

Drusus is sometimes referred to in literature as "Castor"; most notably in the book I, Claudius by Robert Graves.