The Moiety were a group of Rivenese villagers who opposed Gehn's tyrannical reign over the Age of Riven. They often sabotaged Gehn's machines and attacked those who collaborated with Gehn by joining his pseudo-D'ni guilds. They were feared by the rest of the natives, and their ability to evade capture regularly infuriated Gehn.
When Catherine was tricked into returning to Riven in 9462 DE by her sons, the Moiety were able to rescue her from Gehn's bumbling guard, Cho, and brought her to live in the underground network of tunnels which they used as a base of operations. Since she and Atrus imprisoned Gehn on Riven 30 years earlier, she had developed a sort of religious significance to the Moiety. Some of their original number saw her and Atrus confront Gehn at the Star Fissure, and concluded that the two had stripped Gehn of his godly powers. When Catherine returned, they looked to her as a leader, and she orchestrated a plan to have them steal a Descriptive Book and some ink from Gehn so that she could write a new Age for her people to all live in—Tay. Once Tay was completed, the Moiety largely abandoned their underground base. The last remnants of it appear to be a small tunnel leading down to the small cave chamber where the Tay Book was kept, cleverly hidden behind a prison cell wall.