Short answers, pulled from the story.
The first Kingdom Hearts game was released on the 28th of March 2002. This title introduced Sora, Riku, and Kairi to a universe created by Square Enix and The Walt Disney Company under the direction of Tetsuya Nomura.
Tetsuya Nomura created the Kingdom Hearts franchise as a project uniting Square Enix and The Walt Disney Company. He was a young game designer at the time who had never directed a game before the project began.
Kingdom Hearts Chain of Memories was released on the 11th of November 2004 and abandoned traditional action role-playing mechanics for a real-time card game system. This title served as a narrative bridge between the first PlayStation 2 game and Kingdom Hearts II while introducing the concept of Nobodies.
Kingdom Hearts III was released on the 25th of January 2019 in Japan and concluded the Dark Seeker Saga. The game featured a massive cast of characters and culminated in a battle at the Keyblade Graveyard where Xehanort's plan to recreate the χ-blade was thwarted.
Kingdom Hearts IV is set to take place in Quadratum, a realistic world inspired by Tokyo. The story will begin the Lost Master arc and feature Sora, Donald, and Goofy returning to their roles alongside new characters like Yozora.