Marcus Didius Julianus (29 January 133 – 2 June 193) was Roman emperor from March to June 193, during the Year of the Five Emperors. Julianus had a promising political career, governing several provinces, including Dalmatia and Germania Inferior, and defeated the Chauci and Chatti, two invading Germanic tribes. He was even appointed to the consulship in 175 along with Pertinax as a reward, before being demoted by Commodus. After this demotion, his early, promising political career languished.

Julianus ascended the throne after buying it from the Praetorian Guard, who had assassinated his predecessor Pertinax. A civil war ensued in which three rival generals laid claim to the imperial throne. Septimius Severus, commander of the legions in Pannonia and the nearest of the generals to Rome, marched on the capital, gathering support along the way and routing cohorts of the Praetorian Guard Julianus sent to meet him. Abandoned by the Senate and the Praetorian Guard, Julianus was killed by a soldier in the palace and succeeded by Severus.