Galerius (Latin: Gaius Galerius Valerius Maximianus Augustus; c. 260 – April or May 311), was Roman Emperor from 305 to 311. During his reign he campaigned, aided by Diocletian, against the Sassanid Empire, sacking their capital Ctesiphon in 299. He also campaigned across the Danube against the Carpi, defeating them in 297 and 300. Although he was a staunch opponent of Christianity, Galerius ended the Diocletianic Persecution when he issued an edict of toleration in 311.

Galerius was born in Serdica, though some modern scholars consider the strategic site where he later built his palace named after his mother – Felix Romuliana (Gamzigrad) – his birth and funeral place. His father was a Thracian and his mother Romula was a Dacian woman, who left Dacia because of the Carpians' attacks. He originally followed his father's occupation, that of a herdsman, where he got his surname of Armentarius (Latin: armentum, herd).

He served with distinction as a soldier under Emperors Aurelian and Probus, and in 293 at the establishment of the Tetrarchy, was designated Caesar along with Constantius Chlorus, receiving in marriage Diocletian's daughter Valeria (later known as Galeria Valeria), and at the same time being entrusted with the care of the Illyrian provinces. After a few years Danube campaign against Sarmatians and Goths he receive a command of the legions on the eastern Imperial limits. Soon after his appointment, Galerius would be dispatched to Egypt to fight the rebellious cities Busiris and Coptos.

Galeria Valeria (died 315) was the daughter of Roman Emperor Diocletian and wife of his co-emperor Galerius.

Born as Valeria to Diocletian and Prisca, she married Galerius in 293, when her father elevated him to the position of Caesar. This marriage was clearly organized to strengthen the bonds between the two emperors.

Galeria was sympathetic towards Christians, while Galerius persecuted them.

Galeria was raised to the title of Augusta and Mater Castrorum in November 308. Since Galerius fathered no child with her, Galeria adopted her husband's illegittimate son, Candidianus, as her own.

When Galerius died, in 311, Licinius was entrusted with the care of Valeria and her mother Prisca. The two women, however, fled from Licinius to Maximinus Daia, whose daughter was betrothed to Candidianus. After a short time, Valeria refused the marriage proposal of Maximinus, who arrested and confined her in Syria and confiscated her properties. At the death of Maximinus, Licinius ordered the death of both women. Valeria fled, hiding for a year, until she was found in Thessaloniki. She was captured by the mob, beheaded in the central square of the city, and her body thrown in the sea. She was canonized as a Christian saint with her mother (see Saint Alexandra).