Who is True Voice of the Tree Het Masteen. from The Rise of Endymion and what is their importance?

True Voice of the Tree Het Masteen is one of the original Hyperion pilgrims. He is a Templar, who was kidnapped by the Shrike while on pilgrimage, and who was subsequently carried forward into the future to pilot his treeship the Yggdrasill on a tour of the Pax. His primary goal is to aid Aenea in her mission.