Otho was born into a family that had held the consulship under Augustus. He married Poppaea Sabina, but when the emperor Nero took Poppaea for his mistress--she later became his wife--Otho was sent from Rome to govern Lusitania (58). For 10 years he ruled this province with integrity. Then, in 68, Otho joined the rebellion against Nero led by Galba, governor of the neighbouring province of Tarraconensis. He had hoped to be designated Galba's successor, but when Galba disappointed him by adopting Lucius Piso Licinianus (January 69), Otho prepared to seize power. The Praetorian Guard rebelled, Galba and Piso were murdered in the Forum, and Otho was acclaimed emperor (January 15).
Before Galba's death, however, the legions in Germany had declared for Aulus Vitellius, whose troops were already moving toward Italy. Acting with speed and determination, Otho sent a naval expedition to Narbonensis (a region in southern Gaul), summoned the Danube legions, and himself marched out on March 14. Although substantial forces joined Otho from Illyricum, by early April the Vitellian forces were far stronger. Experienced advisers counseled delay, but Otho insisted on action. His army was completely defeated east of Cremona, and Otho committed suicide. (Encyclopedia Britannica)
Marcus Salvius Otho, Roman emperor from January to April 69.