Constantine the Great
Gaius Flavius Valerius Aurelius Constantinus (In Latin Constantine's official imperial title was IMPERATOR CAESAR FLAVIVS CONSTANTINVS PIVS FELIX INVICTVS AVGVSTVS, Imperator Caesar Flavius Constantine Augustus, the pious, the fortunate, the undefeated. After 312, he added MAXIMVS ("the greatest"), and after 325 replaced invictus ("undefeated") with VICTOR, as invictus reminded of Sol Invictus, the Sun God.)

February 27, 272–May 22, 337, commonly known as Constantine I, Constantine the Great, or (among Eastern Orthodox and Eastern Catholic Christians) Saint Constantine, was a Roman Emperor, proclaimed Augustus by his troops on July 25, 306 and who ruled an ever-growing portion of the Roman Empire until his death.

Constantine was born at Naissus (modern Niš, Serbia) in the province of Moesia Superior, to Roman general, Constantius Chlorus, and his first wife Helena, an innkeeper's daughter who at the time was only sixteen years old. His father left his mother around 292 to marry Flavia Maximiana Theodora, daughter or step-daughter of the Western Roman Emperor Maximian. Theodora would give birth to six half-siblings of Constantine, including Julius Constantius.
In 324 AD, Constantine finally achieved full control over an undivided empire. He re-located the imperial headquarters to Byzantium, and changed the name of the city to Constantinople (present-day İstanbul) as the capital of the Roman Empire .
In 326, Constantine had his eldest son Crispus tried and executed, as he believed accusations that Crispus had an affair with Fausta, Constantine's second wife. A few months later he also had Fausta killed as the apparent source of these false accusations.He was succeeded by his three sons by Fausta, Constantine II, Constantius II, and Constans. A number of relatives were murdered by followers of Constantius. He also had two daughters, Constantina and Helena, wife of Emperor Julian.
Constantine was not only the first Christian Emperor, but he was the greatest of all Roman Emperors.