Tiberius Claudius Caesar Augustus Germanicus was Roman emperor, ruling from AD 41 to 54. A member of the Julio-Claudian dynasty,  Claudius was born to Drusus and Antonia Minor at Lugdunum in Roman Gaul, where his father was stationed as a military legate. He was the first Roman emperor to be born outside Italy.

As he had a limp and slight deafness due to sickness at a young age, he was ostracized by his family and was excluded from public office until his consulship (which was shared with his nephew, Caligula, in 37). Claudius's infirmity probably saved him from the fate of many other nobles during the purges throughout the reigns of Tiberius and Caligula, as potential enemies did not see him as a serious threat. His survival led to his being declared emperor by the Praetorian Guard after Caligula's assassination, at which point he was the last adult male of his family.

Despite his lack of experience, Claudius was an able and efficient administrator. He expanded the imperial bureaucracy to include freedmen, and helped restore the empire's finances after the excesses of Caligula's reign. He was also an ambitious builder, constructing new roads, aqueducts, and canals across the Empire. During his reign, the Empire started its successful conquest of Britain. Having a personal interest in law, he presided at public trials, and issued edicts daily. He was seen as vulnerable throughout his reign, particularly by elements of the nobility. Claudius was constantly forced to shore up his position, which resulted in the deaths of many senators. Those events damaged his reputation among the ancient writers, though more recent historians have revised that opinion. Many authors contend that he was murdered by his own wife, Agrippina the Younger. After his death at the age of 63, his grandnephew and legally adopted step-son, Nero, succeeded him as emperor.

Claudius wrote copiously throughout his life. Arnaldo Momigliano states that during the reign of Tiberius, which covers the peak of Claudius's literary career, it became impolitic to speak of republican Rome. The trend among the young historians was either to write about the new empire or about obscure antiquarian topics. Claudius was the rare scholar who covered both.

The influence of historical study on Claudius is obvious. In his speech on Gallic senators, he uses a version of the founding of Rome identical to that of Livy, his tutor in adolescence. The speech is meticulous in details, a common mark of all his extant works, and he goes into long digressions on related matters. This indicates a deep knowledge of a variety of historical subjects that he shared. Many of the public works instituted in his reign were based on plans first suggested by Julius Caesar. Levick believes this emulation of Caesar may have spread to all aspects of his policies.

Claudius was criticized for  being dominated by women and wives, and of being a womanizer.

Claudius married four times, after two failed betrothals. The first betrothal was to his distant cousin Aemilia Lepida, but was broken for political reasons. The second was to Livia Medullina Camilla, which ended with Medullina's sudden death on their wedding day.

Claudius' first wife was Plautia Urgulanilla,  the granddaughter of Livia's confidant Urgulania. During their marriage she gave birth to a son, Claudius Drusus. Drusus died of asphyxiation in his early teens, shortly after becoming engaged to Junilla, daughter of Sejanus.

Claudius later divorced Urgulanilla for adultery and on suspicion of murdering her sister-in-law Apronia. When Urgulanilla gave birth after the divorce, Claudius repudiated the baby girl, Claudia, as the father was allegedly one of his own freedmen. Later, this action made him the target of criticism by his enemies.  Soon after, (possibly in 28) Claudius married Aelia Paetina, a relative of Sejanus, if not Sejanus's adoptive sister. During their marriage, Claudius and Paetina had a daughter, Claudia Antonia. He later divorced her after the marriage became a political liability. One version suggests that it may have been due to emotional and mental abuse by Paetina.

Some years after divorcing Aelia Paetina, in 38 or early 39, Claudius married Valeria Messalina, who was his first cousin once removed (Claudius's grandmother, Octavia the Younger, was Valeria's great-grandmother on both her mother and father's side) and closely allied with Caligula's circle. Shortly thereafter, she gave birth to a daughter, Claudia Octavia. A son, first named Tiberius Claudius Germanicus, and later known as Britannicus, was born just after Claudius's accession.

This marriage ended in tragedy. The ancient historians allege that Messalina was a nymphomaniac who was regularly unfaithful to Claudius—Tacitus states she went so far as to compete with a prostitute to see who could have more sexual partners in a night – and manipulated his policies to amass wealth. In 48, Messalina married her lover Gaius Silius in a public ceremony while Claudius was at Ostia.

Sources disagree as to whether or not she divorced the Emperor first, and whether the intention was to usurp the throne. Under Roman law, the spouse needed to be informed that he or she had been divorced before a new marriage could take place; the sources state that Claudius was in total ignorance until after the marriage.  Scramuzza, in his biography, suggests that Silius may have convinced Messalina that Claudius was doomed, and the union was her only hope of retaining her rank and protecting her children. The historian Tacitus suggests that Claudius's ongoing term as Censor may have prevented him from noticing the affair before it reached such a critical point, after which she was executed.

Claudius married once more. Ancient sources tell that his freedmen put forward three candidates, Caligula's third wife Lollia Paulina, Claudius's divorced second wife Aelia Paetina and Claudius's niece Agrippina the Younger. According to Suetonius, Agrippina won out through her feminine wiles. She gradually seized power from Claudius and successfully conspired to eliminate his son's rivals, opening the way for her son to become emperor.

Sculpture of Agrippina crowning her young son Nero (c. AD 54–59)
The truth is probably more political. The attempted coup d'état by Silius and Messalina probably made Claudius realize the weakness of his position as a member of the Claudian (but not the Julian) family. This weakness was compounded by the fact that he did not yet have an obvious adult heir, Britannicus being just a boy. Agrippina was one of the few remaining descendants of Augustus, and her son Lucius Domitius Ahenobarbus (the future Nero) was one of the last males of the Imperial family. Coup attempts might rally around the pair and Agrippina was already showing such ambition. It has been suggested that the Senate may have pushed for the marriage, an attempt to end the feud between the Julian and Claudian branches.

This feud dated back to Agrippina's mother's actions against Tiberius after the death of her husband Germanicus (Claudius's brother), actions that Tiberius had punished. In any case, Claudius accepted Agrippina and later adopted the mature Ahenobarbus as his son, renaming him as 'Nero Claudius Caesar'.

Nero was married to Claudius's daughter Octavia, made joint heir with the underage Britannicus, and promoted; Augustus had similarly named his grandson Postumus Agrippa and his stepson Tiberius as joint heirs, and Tiberius had named Caligula as his joint heir with his grandson Tiberius Gemellus. Adoption of adults or near adults was an old tradition in Rome when a suitable natural adult heir was unavailable, as was the case during Britannicus's minority. Claudius may have previously looked to adopt one of his sons-in-law to protect his own reign.

Ancient historians agree that Claudius was murdered by poison – possibly contained in mushrooms or on a feather (ostensibly put down his throat to induce vomiting) – and died in the early hours of 13 October 54.

Nearly all implicate his final and powerful wife, Agrippina, as the instigator. Agrippina and Claudius had become more combative in the months leading up to his death. This carried on to the point where Claudius openly lamented his bad wives, and began to comment on Britannicus' approaching manhood with an eye towards restoring his status within the imperial family. Agrippina had motive in ensuring the succession of Nero before Britannicus could gain power.

Some implicate either his taster Halotus, his doctor Xenophon, or the infamous poisoner Locusta as the administrator of the fatal substance. Some say he died after prolonged suffering following a single dose at dinner, and some have him recovering only to be poisoned again. Among his contemporary sources, Seneca the Younger ascribed the emperor's death to natural causes, while Josephus only spoke of rumors of his poisoning.

Some historians have cast doubt on whether Claudius was murdered or merely died from illness or old age. Evidence against his murder include his serious illnesses in his last years, his unhealthy lifestyle and the fact that his taster Halotus continued to serve in the same position under Nero. Claudius had been so ill the year before that Nero vowed games for his recovery and the year of 54 seems to have been such an unhealthy year that one sitting member of each magistracy died within the span of a few months. He may even have died by eating a naturally poisonous mushroom, possibly Amanita muscaria. On the other hand, some modern scholars claim the near universality of the accusations in ancient texts lends credence to the crime.