The unstoppable juggernaut is first attested in English in a 1638 article, a transliteration of the name of the regional Hindu deity ଜଗନ୍ନାଥ (Jagannātha). For the next 200 years, it’s only seen as a proper noun referring to this specific deity, mostly centered around the annual Ratha Yatra festival in Puri, a city on the east coast of India. The festival includes a procession of massive (40’/15m) horse-drawn chariots, with the largest and grandest devoted to Jagannath.
Held annually since 1460, this festival left such an impression on English observers that the name Jagannath itself came to stand for the unstoppable momentum of its lead chariot. Beginning in 1854, “Jaggernaut” became a metaphor for inexorability, its ending now influenced by the English suffix -naut. It became a fully lowercase common noun used to describe any gigantic heavy vehicle by the mid-1900s, in addition to the unstoppable metaphorical use.
Its most familiar use today originates with the Marvel villain Juggernaut, introduced in a 1965 X-Men comic book and perhaps most well known for the “Nothing Can Stop the Juggernaut!” storyline in 1982 Spider-Man comics.
Jagannath’s name originates from Sanskrit जगन्नाथ (jagannātha), meaning “lord of the universe”, from जगन् (jágan) “world” + नाथ (nāthá) “lord”.