Drusus was a cognomen in Ancient Rome originating with the Livii. Under the Republic, it was the intellectual property and diagnostic of the Livii Drusi. Under the empire and owing to the influence of an empress, Livia Drusilla, the name was used for a branch of the Claudii into which she had married: the Claudii Drusi. During that period, when a line reached two or three branches calling for four or five names, the Romans shortened to one or two; consequently, "Drusus" could seem to be used in place of a praenomen. True praenomina, however, could be assigned to anyone within the customary usage of their clan, but Drusus could only be used in lines that had it as an agnomen.
Male members of the Livii Drusi, a branch of the Livia gens:
- Gaius Livius Drusus, consul in 147 BC
- Marcus Livius Drusus,the name of two Republican politicians:
- Marcus Livius Drusus (consul) (died 108 BC), father
- Marcus Livius Drusus (tribune) (died 91 BC), son
- Marcus Livius Drusus Claudianus (died 42 BC), adopted from the Claudii (hence Claudianus) by the tribune and the father of Livia Drusilla, Augustus' third wife
- Marcus Livius Drusus Libo (born 1st-century BC), adopted by Claudianus from the Scribonii Libones (hence Libo), consul in 15 BC
Male members of other clans whose mother belonged to the Livii Drusi and had given her son the agnomen Drusus in commemoration of that fact, even though he was not by law of the Livii Drusi. The most noted example is perhaps the Claudii Drusi, who were given the name Drusi by their mother Livia Drusilla. They were not Livii Drusi, but a new branch of the Claudii.
- Nero Claudius Drusus Germanicus, the brother of Tiberius. Also called Drusus I.
- Tiberius Claudius Drusus, the birth name of emperor Claudius. He was the son of Nero Claudius Drusus.
- Drusus Julius Caesar (13 BC–23 AD), son of Tiberius. Also called Drusus II or Drusus Minor.
- Marcus Scribonius Libo Drusus, a grandson of Pompey who in AD 16 was charged with plotting against Tiberius, Germanicus, and Drusus Julius Caesar
- Drusus Julius Caesar (7–33 AD), son of Germanicus. Also called Drusus III.
- Nero Claudius Caesar Drusus Germanicus (37–68 AD), adoptive name of emperor Nero
- Drusus Claudius Nero, the name of two prominent Roman citizens