Call of Cthulhu is a Lovecraftian horror TTRPG published by Chaosium in 1981 and designed by Sandy Petersen. It runs on a percentile (d100) system built atop Chaosium’s Basic Role-Playing (BRP).
Players take the role of Investigators rather than heroes, losing Sanity as they uncover Mythos truths instead of accumulating power. This structure — the more you learn, the more you break — is the heart of how cosmic horror was translated into rules, running in the opposite direction from dungeon fantasy’s growth curve.