Valentinus, sometimes anglicized as Valentine, was a Byzantine usurper of probable Armenian extraction, who served under emperor Constans II from 641 until 644 or 645. He rose to prominence under Heraclius Constantine, who appointed him to secure the succession of his son Heraclius to the throne, at the cost of Heraclonas and Martina. Valentinus managed to successfully depose them, along with Heraclonas's brothers David Tiberius and Martinus; this left Constans as sole ruler. Valentinus became the boy's regent, becoming the most powerful man in the empire. Following a failed military campaign against the Arabs, ties between him and Constans became increasingly hostile, such that in 644 or 645, Valentinus attempted to become augustus (emperor) and depose Constans. This failed, and Valentinus was lynched along with his envoy Antoninus.

David was one of three co-emperors of Byzantium for a few months in late 641, and had the regnal name Tiberius. David was the son of Emperor Heraclius and his wife and niece Empress Martina. He was born after the emperor and empress had visited Jerusalem and his given name reflects a deliberate attempt to link the imperial family with the Biblical David. The David Plates, which depict the life of King David, may likewise have been created for the young prince or to commemorate his birth. David was given the senior court title caesar in 638, in a ceremony during which he received the kamelaukion cap previously worn by his older brother Heraclonas.