The Ancient and the Lost is the first WarClans Book for the RuneSlayer roleplaying game, and details the WarClans of the Elves, Dwarves, and Tuathae; introduces the Merfolk races and its WarClans; and includes four new human WarClans.

Like the other RuneSlayer supplements, The Ancient and the Lost uses the old name for the RPG, RuneQuest: Slayers. Originally intended for publication by Avalon Hill in 1998, but the game line was canceled and the supplement was later released as a free PDF.