USD, aka "Dollar Big Brother," is the globally recognized United States Dollar, widely used in international trade and reserves. USDT, or Tether USD (Tai Da Coin), aims to maintain a 1:1 peg with the USD in the cryptocurrency world, but faces trust issues. USDC, or USD Coin, is a new stablecoin launched by Circle and Coinbase, with high transparency, supporting multiple blockchain networks for faster, cheaper transactions, gaining popularity. Despite similar names, they each have unique characteristics and purposes, playing important roles in the cryptocurrency world and offering investors more choices and convenience.