Servius Galba was born December 24, 3 B.C., in Tarracina, the son of C. Sulpicius Galba and Mummia Achaica. Galba served in civil and military positions throughout the reigns of the Julio-Claudian emperors, but when he (then governor of Hispania Tarraconensis) became aware that Nero wanted him killed, he rebelled. Galba's agents won over to their side Nero's praetorian prefect. After Nero committed suicide, Galba, who was in Hispania, became emperor, coming to Rome in October 68, in the company of Otho, governor of Lusitania. Although there is debate as to when Galba actually assumed power, taking titles of emperor and caesar, there is a dedication from October 15, 68 about the restoration of liberty.
Galba antagonized many, including Otho, who promised financial rewards to the praetorians in exchange for their support. They declared Otho emperor on January 15, 69, and killed Galba.
See: "The Emperor Galba's Assumption of Power: Some Chronological Considerations," by Arcadio del Castillo. Historia: Zeitschrift für Alte Geschichte, Vol. 51, No. 4 (4th Qtr., 2002), pp. 449-461.