Which Animal Crossing game introduced Isabelle?

Animal Crossing: New Leaf introduced Isabelle.

Isabelle first appeared in Animal Crossing: New Leaf, released for the Nintendo 3DS beginning in Japan in November 2012 and in Western regions in 2013. In the game, she serves as the player’s assistant after the player becomes mayor of the town.

Her role was designed around the needs of a player-controlled mayor. Isabelle helps with town advice, public works, ordinances, ceremonies, and daily announcements. Her friendly personality, loyalty, and occasional clumsiness quickly made her one of the series’ most recognizable characters.

Players sometimes associate her debut with New Horizons because she became highly visible there, but New Horizons was her return, not her introduction. She also appeared in spin-offs and crossed into other Nintendo games, including Super Smash Bros. Ultimate. Her Japanese name is Shizue, while “Isabelle” is the localized English name.