Flavius Heraclius Constantinus Augustus (Greek: Φλάβιος Ηράκλειος Κωνσταντίνος Αύγουστος), known as Constans II, was Roman Emperor from AD 641 to 668. The grandson of Heraclius I, he succeeded the latter after a period of civil strife during which several emperors, including Constan's father Constantine III, took the throne and were soon overthrown. Constans II became sole emperor at the age of 11 and initially ruled through a regency led by Paul II, Patriarch of Constantinople, and the general Valentinus.
In 644 Valentinus attempted to seize power for himself but failed. This event increased Constans' standing among the populace of Constantinople and enabled him to take power two years later.
As an adult, Constans tried to enforce a policy of religious toleration throughout the empire to avoid a repeat of the devastating civil war that had shaken his grandfather's reign. He refused to persecute either Christianity or Islam, and even resorted to forbidding by decree any further discussion concerning the reality or otherwise of the Trinity. Naturally this middle path failed to satisfy extremists on both sides, but Constans cleverly managed to make the dissidents vanish without accidentally creating any martyrs. It's unknown what his own personal religious beliefs were.
Constans II was assassinated in his bath on the 15th September 668, amid rumours that he intended to move the capital to Antioch. He was succeeded by his son Constantine IV, under whom the rumour ironically came true with the loss of Constantinople to the Bulgars.