The Thai baht fell sharply after Thailand abandoned its fixed exchange rate during the 1997 Asian financial crisis. On 2 July 1997, Thailand allowed the baht to float after sustained pressure from currency speculators and dwindling foreign-exchange reserves.
The baht’s devaluation made dollar-denominated debts more expensive for Thai companies and banks. Investors then reassessed other Asian economies, causing capital flight, falling stock markets, banking stress, and currency devaluations across the region.
Indonesia, South Korea, and Malaysia were also severely affected, but their currencies were not the first one at the center of the crisis. The Thai baht is therefore the precise answer to this question.
The International Monetary Fund later organized major assistance programs for Thailand, Indonesia, and South Korea. The crisis spread well beyond stock exchanges because exchange rates, corporate borrowing, and banking systems were tightly connected.