Martinus or Marinus was caesar of the Byzantine Empire from c. 639 to 641. Martinus was the fifth son of Emperor Heraclius and Empress Martina, who was Heraclius' second wife and niece. Martinus was elevated to caesar, a junior imperial title that placed him on the line of succession, at some point between 638 and 640 by his father.

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.