Traveller

Traveller is the classic science-fiction tabletop RPG published by Game Designers' Workshop in 1977 — the sci-fi RPG that made Star Wars-style space adventure a tabletop staple. Its 2d6-plus-modifier resolution system is famously simple, and its character-generation system is famously deadly: your character can die of old age or during their military career before the game even starts. Multiple editions and the popular Third Imperium setting.