The word enters European languages through the Crusades: medieval Latin and Italian chroniclers wrote assissini and assassini for the Nizari Ismailis of Syria, the mountain state Hasan-i Sabbah founded at Alamut in 1090. Their operatives called themselves fida'i, self-sacrificers, and their method was public, patient, political killing: the Seljuk vizier Nizam al-Mulk in 1092 is the first famous corpse. The Mongols took Alamut in 1256, and the historian Juwayni, who catalogued the fortress as it fell, described its library and storerooms in detail and mentioned no garden.
Marco Polo's Travels gave Europe the full legend: the Old Man of the Mountain drugged young men with hashish, woke them in a walled garden of wine and maidens, told them this was paradise, and promised readmission if they died on his missions. The tale explains the etymology Europe settled on: hashishiyya, the hashish-users, worn down to assassin.
Farhad Daftary's The Assassin Legends (1994) went through the Nizari and anti-Nizari sources alike: no Ismaili text mentions hashish, and in Syrian usage hashishiyya was a slur meaning roughly low-class rabble, not a pharmacy report. Daftary's verdict: the drug tales and the paradise garden were fabricated and circulated by Europeans, building on Sunni polemic. De Sacy's 1818 Memoire had already canonized the hashish reading; the counter-reading is that the word's origin story is itself the oldest disinformation campaign in this archive.
If the name is an insult, the hashish is a smear, and the paradise garden never existed, what part of the story we all know is true?