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.

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.