The old man of the mountain

Needs Roads to Power (Hasan's story is landless-adventurer content), must be done in Hasan-i Sabbah's own lifetime, 1066 start. His story has a hidden tracker: stay in Persia, build piety (pilgrimages, the Prolific Pilgrims perk) and your forces, and do NOT evangelize yet. You'll be called to Cairo - build the biggest army you can and wait for the Egyptian Caliph to die, converting to Nizarism when the event allows; always pick the options that advance the path. Back in Persia, NOW evangelize hard (your special soldiers scale with counties of your faith in the realm). When the Persian Emperor dies, decline the "enemy of the faith" prompt until his weaker young successor is the target, found the Assassins, wait for a civil war, and launch the revolution - usually a walkover while the emperor fights his own vassals. (If this appears twice in the list, it's the same achievement under two capitalisations - one unlock covers it.)