Who is Holsten Mason in the novel, Children of Time?

Holsten Mason is a classicist on the Gilgamesh who is the only true master of Old Empire technology, language, and history left in the human species. While he is constantly referred to as the oldest man in the world as he is out of cryo sleep more than the other humans, it is implied that other characters, such as Guyen and Lain, are secretly out more than he is between journeys.