In which game did the Konami Code make its first appearance?

The Konami Code made its first appearance in the game Gradius. Originally developed by Kazuhisa Hashimoto, the code was implemented as a cheat to aid him during testing for the game. The famous code, Up, Up, Down, Down, Left, Right, Left, Right, B, A, allowed players to receive a full set of power-ups, making the game significantly easier. The Konami Code gained popularity due to its use in various Konami games and has since become a well-known gaming phenomenon, often referenced and celebrated in popular culture.