Ahenobarbus was a cognomen used in ancient Rome meaning "gold beard." Its use seems to have been reserved exclusively for men of the Domitii gens (family), who may have received it in the early years of the Roman Republic. For those unfamiliar with the Roman system of naming, most men had three names: the praenomen, which was the equivalent of a first name; the nomen, which was the equivalent of a modern surname (which described the aforementioned gens); and a cognomen, which was something like a more specific surname either given to or adopted by one member of a certain gens for the purposes of differentiation. For example, the gens Junii was one of the oldest in Rome (with ties to the Etruscan kings), and had many branches. One member, Lucius Junius, was ironically given the cognomen "Brutus," which meant "simple" or "stupid," in recognition of his legendary shrewdness (think of huge tough guys being given the nickname "Tiny"). His direct descendants were thus both Junii and Brutii, including his famous descendant Marcus Junius Brutus.
The men of the Domitii who were from the Ahenobarbus branch were all given one of two praenomina: Gnaeus and Lucius. The reasons for this are somewhat obscure, but one story seems to have it that the first distinguished members of the branch lived during the early to middle Republican era and were either two brothers or a father and son with those respective names. Either way, the pattern was firmly and irrevocably established by the second century BC and all Ahenobarbi after this point are demonstrably named Lucius or Gnaeus. The first known Ahenobarbus of consular rank was a Gnaeus, who served in that position in 192 BC, apparently against the opposition of Scipio Africanus, who was at that time the first man in Rome given his nation-saving defeat of Hannibal in the Second Punic War. This makes his election all the more impressive and improbable; a comparable hypothetical upset would have been Michael Dukakis defeating George Bush in the presidential election of 1988. The Ahenobarbi had officially arrived as players in the Roman political scene.
This Gnaeus' grandson, also named Gnaeus, was elected consul in 122 BC and received a triumph (the highest military honor of ancient Rome) for his successes in Gaul. His son of the same name was to date the most accomplished member of the family, having held the offices of Tribune of the plebs, pontifex maximus (chief priest), consul (96 BC), and finally censor, the most senior office of the Republic. The consuls had all the executive authority, but it was the censors who were responsible for maintaining public morality and carrying out the census. This is significant because the Roman census did not just record residency, it recorded class. A patrician who fell out of favor with a given censor could find himself demoted to the rank of equestrian or even plebeian or could be kicked out of the Roman Senate for engaging in poor public behavior (for example, Cato removed a man from the Senate for kissing his wife on the cheek in public!). This Gnaeus' brother, Lucius, was consul for the year 94 BC.
The Ahenobarbi, like the rest of the Roman aristocracy, were forced to choose sides in the civil war between Gaius Julius Caesar and Gnaeus Pompeius Magnus in the first century BC. A certain Lucius (consul 54 BC) and his son Gnaeus (consul 32 BC) supported Pompey against Caesar, the former going so far as to command a Pompeian legion at the Battle of Pharsalus and dying there in 48 BC. His son abandoned Pompey and threw his lot in with Caesar, who won the war. After Caesar's assassination, Gnaeus allied himself with the Liberatores, (i.e. his cousin Brutus and Gaius Longinus Cassius), but later switched sides and joined Marcus Antonius and the forces of the Second Triumvirate. When Antonius and Gaius Julius Caesar Octavianus, the grand nephew and adopted son of Julius Caesar, came to blows, Gnaeus joined Octavian but died in 31 BC shortly after the conclusion of the war. Gnaeus' son, Lucius, was consul in the year 16 BC, and earned a reputation for bizarre and vexatious behavior that disgusted many of his contemporaries (but not, apparently, the Emperor Augustus, who named him in his will). Lucius' son, Gnaeus, was consul in 32 AD, and was married to Agrippina the Younger, the sister of the future Emperor Caligula. His reputation is similar to that of his father's, known as he was for his spitefulness and indolence.
The most famous Ahenobarbus is Lucius, the son of the most recently mentioned Gnaeus and his wife Agrippina, although history does not remember him by that name. Gnaeus died in 40 AD and his brother-in-law, the Emperor, was killed the following year. Caligula was succeeded by his uncle Claudius, who was a competent administrator but a horrible judge of character with a weakness for manipulative women. After a series of failed marriages, Claudius was seduced by his niece Agrippina, who eventually convinced him to adopt her son (his grand nephew) Lucius as his chief beneficiary (and primary successor) over his own biological son. Claudius, drunk with lust, relented and following Roman adoption convetions, Lucius Domitius Ahenobarbus became known as Nero Claudius Caesar Germanicus, usually known just by the name Nero. Nero succeeded Claudius after his mother allegedly poisoned the latter, and was considered an acceptable candidate for the highest office in the land because of his genetic acceptability (he was one of two living male blood descendants of Augustus; the other died under mysterious circumstances). Nero, of course, is famous for arranging the murder of his mother, subjecting the Roman populace to his singing and lyre-playing, starting the first major persecution of Christians in the Empire, and coopting a third of the city of Rome's public property for his own use after the Great Fire. Nero committed suicide in 68 after a widespread rebellion exploded against him with the words "what an artist the world is losing in me!"
The Ahenobarbi do not appear in the historical record after the death of Nero. The broader Domitii gens, however, continued to be prominent in Roman politics, with the emperors Titus and Domitian being distantly related to the clan on their mother's side and the third century-era barracks emperor Aurelian being a true, blue Domitius.