Galba (/ˈɡælbə/ GAL-bə; born Servius Sulpicius Galba; 24 December 3 BC – 15 January AD 69) was Roman emperor, ruling for 7 months from 8 June AD 68 to 15 January 69. He was the first emperor in the Year of the Four Emperors and assumed the throne following Emperor Nero's suicide.

Born into a wealthy family, Galba held at various times the positions of praetor, consul, and governor of the provinces of Gallia Aquitania, Germania Superior, and Africa during the first half of the first century AD. He retired from his positions during the latter part of Claudius' reign (with the advent of Agrippina the Younger), but Nero later granted him the governorship of Hispania. Taking advantage of the defeat of Vindex's rebellion and Nero's suicide, he became emperor with the support of the Praetorian Guard.

Galba's physical weakness and general apathy led to his rule being dominated by favorites. Unable to gain popularity with the people or maintain the support of the Praetorian Guard, Galba was murdered on the orders of Otho, who became emperor in his place.

Galba was not related to any of the emperors of the Julio-Claudian dynasty, but he was a member of a distinguished noble family. The origin of the cognomen Galba is uncertain. Suetonius offers a number of possible explanations; the first member of the gens Sulpicia to bear the name might have gotten the name from the term galba, which the Romans used to describe the Gauls, or after an insect called galbae. One of Galba's ancestors had been consul in 200 BC, and another of his ancestors was consul in 144 BC; the later emperor's father and brother, both named Gaius, would hold the office in 5 BC and AD 22 respectively. Galba's grandfather was a historian and his son was a barrister whose first marriage was to Mummia Achaica, granddaughter of Quintus Lutatius Catulus and great-granddaughter of Lucius Mummius Achaicus; Galba prided himself on his descent from his great-grandfather Catulus. According to Suetonius, he fabricated a genealogy of paternal descent from the god Jupiter and maternal descent from the legendary Pasiphaë, wife of Minos. Reportedly, Galba was distantly related to Livia to whom he had much respect and in turn by whom he was advanced in his career; in her will she left him fifty million sesterces; Emperor Tiberius however cheated Galba by reducing the amount to five hundred thousand sesterces and never even paid Galba the reduced amount.

Servius Sulpicius Galba was born near Terracina on 24 December 3 BC. His elder brother Gaius fled from Rome and committed suicide because the emperor Tiberius would not allow him to control a Roman province. Livia Ocellina became the second wife of Galba's father, whom she may have married because of his wealth; he was short and hunchbacked. Ocellina adopted Galba, and he took the name "Lucius Livius Ocella Sulpicius Galba", although he probably kept his original name in unofficial context, as evidenced by the fact that he reverted to it upon his accession as emperor. Galba preferred males over females in terms of sexual attraction; according to Suetonius, he "preferred full-grown, strong men". Nevertheless, he married a woman named Aemilia Lepida and had two sons. Aemilia and their sons died during the early years of the reign of Claudius (r. 41–54). Galba would remain a widower for the rest of his life.

Galba became praetor in about 30, then governor of Aquitania for about a year, then consul in 33. In 39 the emperor Caligula learned of a plot against himself in which Gnaeus Cornelius Lentulus Gaetulicus, the general of the legions of Germania Superior, was an important figure; Caligula installed Galba in the post held by Gaetulicus. According to one report Galba ran alongside Caligula's chariot for twenty miles. As commander of the legions of Germania Superior, Galba gained a reputation as a disciplinarian. Suetonius writes that Galba was advised to take the throne following the assassination of Caligula in 41, but loyally served Caligula's uncle and successor Claudius (r. 41–54); this story may simply be fictional. Galba was appointed as governor of Africa in 44 or 45. He retired at an uncertain time during the reign of Claudius, possibly in 49. He was recalled in 59 or 60 by the emperor Nero (r. 54–68) to govern Hispania.

A rebellion against Nero was orchestrated by Gaius Julius Vindex in Gaul on the anniversary of the death of Nero's mother, Agrippina the Younger, in 68. Shortly afterwards Galba, in rebellion against Nero, rejected the title "General of Caesar" in favor of "General of The Senate and People of Rome". He was supported by the imperial official Tigellinus. At midnight on 8 June, another imperial official, Nymphidius Sabinus, falsely announced to the Praetorian Guard that Nero had fled to Egypt, and the Senate proclaimed Galba emperor. Nero then committed assisted suicide with help from his secretary.

Upon becoming emperor, Galba was faced by the rebellion of Nymphidius Sabinus, who had his own aspirations for the imperial throne. However, Sabinus was killed by the Praetorians before he could take the throne. While Galba was arriving to Rome with the Lusitanian governor Marcus Salvius Otho, his army was attacked by a legion that had been organized by Nero; a number of Galba's troops were killed in the fighting. Galba, who suffered from chronic gout by the time he came to the throne, was advised by a corrupt group which included the general Titus Vinius, commander of one of the legions in Hispania; the praetorian prefect Cornelius Laco; and Icelus, a freedman of Galba. Galba seized the property of Roman citizens, dismissed his Germanic bodyguards, and did not pay the Praetorians and the soldiers who fought against Vindex. These actions caused him to become unpopular.