Tether is a cryptocurrency that had to mirror the USD dollar. It was the major attempt to link cryptocurrencies and fiat currencies. Initially every USDT had to cost $1. Sceptics warned this artificial parity cannot take long.
Till 2019 the situation looked normal, but since that year Tether rejected the idea to mirror USD. The price of the currency fell to $0.74 USDT per one dollar. The currency, however, is still popular, especially as a credit asset.