Short answers, pulled from the story.
Licinius ruled as Roman emperor from 308 to 324, holding authority over the eastern half of the empire for most of that period. Born around 265 into a Dacian peasant family in Moesia Superior, he rose through his close friendship with the emperor Galerius. He was executed on Constantine's orders following his surrender at Chrysopolis in 324.
The Edict of Milan was a joint proclamation issued by Licinius and Constantine I in 313 establishing religious freedom throughout the Roman Empire. It allowed any person to practice any religion, ordered the return of properties confiscated from Christian communities, and freed Christian clergy from civic financial obligations. The text, preserved by the scholar Lactantius, expressed a wish to propitiate 'any Divinity whatsoever in the seat of the heavens'.
At the Battle of Tzirallum on the 30th of April 313, Licinius defeated Maximinus Daza with a force of possibly around 30,000 men against Daza's roughly 70,000. Maximinus had already been weakened by harsh weather on his march from Syria and by the sieges of Byzantium and Heraclea. He escaped disguised as a slave but died in August 313.
The Battle of Chrysopolis, fought near Chalcedon on the 18th of September 324, was Licinius's final stand as Roman emperor. After earlier defeats at the Battle of Adrianople and the Battle of the Hellespont, Licinius made his last stand in Bithynia with the support of the Gothic prince Alica. He surrendered and was initially imprisoned in Thessalonica before being executed.
Licinius's religious allegiance is debated. He co-authored the Edict of Milan, which ended the Great Persecution of Christians, and adopted Christian symbols for his armies. His wife Flavia Julia Constantia was a devout Christian. Eusebius of Caesarea, writing under Constantine's patronage, accused him of later expelling Christians from the palace and ordering pagan military sacrifices, suggesting his beliefs may have changed over time.
Damnatio memoriae is the Latin term for the Roman practice of officially condemning a person's memory. After Licinius's execution, his statues were pulled down and an imperial edict abolished all of his laws and judicial rulings from his entire reign, erasing him from the public record as completely as Roman law allowed.