Publius Helvius Pertinax (1 August 126 – 28 March 193) was Roman emperor for the first three months of 193. He succeeded Commodus to become the first emperor during the tumultuous Year of the Five Emperors.

Born the son of a freed slave, Pertinax became an officer in the army. He fought in the Roman–Parthian War of 161–166, where his success led to higher positions in both the military and political spheres. He achieved the rank of provincial governor and urban prefect. He was a member of the Roman Senate, serving at the same time as the historian Cassius Dio.

When Emoperor Commodus' actions became increasingly erratic in the early 190s, a conspiracy led to his assassination on 31 December 192. The plot was carried out by the Praetorian prefect Quintus Aemilius Laetus, Commodus' mistress Marcia, and his chamberlain Eclectus. After the murder had been carried out, Pertinax, who was serving as urban prefect at this time, was hurried to the Praetorian Camp and proclaimed emperor. His short reign of 87 days was an uneasy one. He attempted to emulate the restrained practices of Marcus Aurelius and made an effort to reform the alimenta, but he faced antagonism from many quarters.

Ancient writers detail how the Praetorian Guard expected a generous donativum on his ascension, and when they were disappointed, agitated until he produced the money, selling off Commodus' property, including the concubines and youths Commodus kept for his sexual pleasures. He reformed the Roman currency dramatically.

Pertinax attempted to impose stricter military discipline upon the pampered Praetorians. In early March he narrowly averted one conspiracy by a group to replace him with the consul Quintus Sosius Falco while he was in Ostia inspecting the arrangements for grain shipments. The plot was betrayed; Falco himself was pardoned but several of the officers behind the coup were executed.

On 28 March 193, Pertinax was at his palace when, according to the Historia Augusta, a contingent of some three hundred soldiers of the Praetorian Guard rushed the gates (two hundred according to Cassius Dio)  Ancient sources suggest that they had received only half their promised pay.  Neither the guards on duty nor the palace officials chose to resist them. Pertinax sent and aide to meet them. who chose to side with the insurgents instead and deserted the emperor.

Although advised to flee, Pertinax then attempted to reason with the insurgents and was almost successful before being struck down by one of the soldiers.  Pertinax must have been aware of the danger he faced by assuming the purple, for he refused to use imperial titles for either his wife or son, thereby protecting them from the aftermath of his own assassination.

After Pertinax's death, the Praetorians auctioned off the imperial title; the winner was the wealthy senator Didius Julianus, whose reign would end mere weeks later with his assassination on 1 June 193.  Julianus was succeeded by Septimius Severus. After he entered Rome, Septimius recognized Pertinax as a legitimate emperor, executed the soldiers who had killed him, and not only pressured the Senate to deify him and provide him a state funeral, but also adopted his cognomen of "Pertinax" as part of his own name.  For some time, he held games on the anniversary of Pertinax's ascension and on his birthday.