Marcus Otho (; born Marcus Salvius Otho; 28 April 32 – 16 April 69) was Roman emperor for three months, from 15 January to 16 April 69. He was the second emperor of the Year of the Four Emperors.

A member of a noble Etruscan family, Otho was initially a friend and courtier of the young emperor Nero until he was effectively banished to the governorship of the remote province of Lusitania in 58 following his wife Poppaea Sabina's affair with Nero. After a period of moderate rule in the province, he allied himself with Galba, the governor of neighbouring Hispania Tarraconensis, during the revolts of 68. He accompanied Galba on his march to Rome, but revolted and murdered Galba at the start of the next year.

Inheriting the problem of the rebellion of Vitellius, commander of the army in Germania Inferior, Otho led a sizeable force which met Vitellius' army at the Battle of Bedriacum. After initial fighting resulted in 40,000 casualties, and a retreat of his forces, Otho committed suicide rather than fight on, and Vitellius was proclaimed emperor.