Short answers, pulled from the story.
Galerius, full name Gaius Galerius Valerius Maximianus, was Roman emperor from 305 to 311. He first served as Caesar under Diocletian from 293 as part of the Tetrarchy, then became Augustus after Diocletian's abdication in 305. He died in late April or early May 311.
Galerius launched his counterattack in the spring of 298 by striking through Armenia rather than across the Mesopotamian plains, using rugged highland terrain that favored Roman infantry over Sasanid cavalry. Local support also gave him the advantage of surprise. During the Battle of Satala, the second of two successive engagements, Roman forces seized Narseh's camp, treasury, harem, and wife.
The Peace of Nisibis, concluded in the spring of 299, made the Tigris the boundary between Rome and Persia. Persia ceded five satrapies to Rome, Armenia returned to Roman control with King Tiridates restored to his throne, and Nisibis became the sole authorized crossing point for trade between the two empires.
Galerius was a fierce advocate of traditional Roman religion and pushed Emperor Diocletian to move against Christianity. The persecutions began with edicts issued on the 24th of February, 303, ordering the destruction of Christian houses of assembly. Some ancient sources accused Galerius of secretly setting fire to the Imperial Palace and blaming Christians, to manufacture a pretext for the crackdown.
The Edict of Serdica, signed by Galerius in April 311 during his final illness, ended the official Roman persecution of Christianity. Galerius acknowledged the policy had failed and called on Christians to pray for the safety of the empire. It was a precursor to the Edict of Milan, issued two years later by Constantine and Licinius, which formally legalized the faith.
Galerius was buried in his mausoleum at Gamzigrad-Romuliana, the palace complex he built near his birthplace in what is now Zaječar, Serbia. Excavations at the site uncovered lumps of corroded iron ring mail, possibly from the wax effigy burned at his imperial funeral. The site was added to the World Heritage List in June 2007.