I believe Nokris is Crota's brother. In Verse 4:10 of the Books of Sorrow, Oryx says [quote]“My son,” he said, “this is your punishment. Come home glorious, or die forgotten!” He picked up Crota by the legs and threw him into the Vex gate network.[/quote] Perhaps this is what happened to Nokris: he failed Oryx, so he was forgotten except for a single statue outside the King's room