Captain Het Masteen, commonly known by his title as the "True Voice of the Tree," is a Templar and the commanding officer of the treeship Yggdrasill. He was born and raised on the Templars' world God's Grove.
He was one of the seven pilgrims sent to Hyperion on the final Shrike pilgrimage. He took the rest of the pilgrims to the planet using his ship, the Yggdrasill. He brought a Möbius Cube containing an erg with him, in the hopes that the creature might prove useful against the Shrike. He was supposed to be the fifth to tell his tale, but before he could do it, he disappeared from the windwagon on the sea of grass, after witnessing the destruction of the Yggdrasill.
His mission was to see his ship destroyed as the prophecies foretold, and to use his erg to gain control of the tree of thorns where the Shrike impales his victims, and to captain it through time.
On that night when the Shrike approached him, he freed the erg locked in the Möbius Cube in order to survive the meeting. He lost consciousness and when he woke up, he was near the Time Tombs. Had nothing to eat, he survived on the snow he found, but when the other pilgrims arrived, he was so weakend he lost consciousness. Father Paul Duré and Sol Weintraub kept him alive with Kassad's FORCE life first aid kits. Waking up in high fever, Masteen saw the tree of the Shrike, and tried to explain his mission but he once again lost consciousness then died.
Paul Duré gave him a funeral service.