Isabelle, a female Shih Tzu-style dog, was first introduced to the Animal Crossing series in New Leaf but has since fast-tracked her way to becoming one of Nintendo's biggest characters. Isabelle is also the fictional head of the Animal Crossing Twitter page, keeping players up to date with the latest happenings in New Horizons and the series in general.
Following her appearances in the Animal Crossing series, she has now made major appearances in other games such as Mario Kart 8 and Super Smash Bros. Ultimate. Returning as the main mascot in a familiar secretary-style role in New Horizons, it's clear Nintendo has an interest in developing her character further than her desk job.
In New Leaf, players first meet Isabelle at the start of the game, where she helps the player move in by offering advice and optional tasks like Tom Nook would have in previous games. Her twin brother Digby is also introduced in the game but has a smaller role as the owner of the Happy Home Showcase. Isabelle can mostly be found in New Leaf in the town hall but is the main character to assist with ceremonies and will stand in the plaza during events. She was also granted the role of reminding the player about saving their game until the Reset Center is built, temporarily replacing Mr. Resetti.
Isabelle also makes appearances in the smaller Animal Crossing releases, Happy Home Designer and Pocket Camp. In Home Designer, her role is very similar to New Leaf, where she gives the player Public Facility projects and, by scanning her Amiibo Card, she will have her own home built that she shares with Digby. In Pocket Camp, she encourages players to make the most out of their campsite by offering tips and providing various goals to achieve. Crafting Isabelle's Slideshow will personally invite her to the player's campsite.
Isabelle's first big breakout from the Animal Crossing Series was being included as a main playable character in Mario Kart 8. Originally included as part of the Animal Crossing x Mario Kart 8 DLC, both her and two Villagers are included to race. She mainly uses the City Tripper bike, and her stats in the Switch version are compatible with the likes of Toadette and Wendy. This was a breakthrough for Isabelle's development as she was not only included in Mario Kart 8 but brought back a second time for the Switch version over older main characters of Animal Crossing such as Tom Nook.
Isabelle's first appearance in Super Smash Bros was as an assist trophy in the Nintendo 3DS version. She returned as a playable character in Super Smash Bros. Ultimate with moves similar to the Villager, where she uses a Fishing Rod as a special side move. All of her features in the game still heavily revolve around the Animal Crossing series, such as her entrance being from the Town Hall and her final smash being Dream Town Hall, where Tom Nook and his nephews show up to trap opponents in the Hall before it explodes. Her appearance is also based on her uniform and characteristics from New Leaf.
In Animal Crossing: New Horizons, Isabelle returns to her role as secretary for Tom Nook. Assisting the player with things like the island's status, Isabelle encourages the development of a beautiful island for everyone to enjoy and offers tips and solutions to help with this. Although working for Nook, Isabelle is more at the forefront of the game as she makes the daily announcements. When the player starts the game for the first time that day, she will read out the date and time and any special events going on that day. If there are no special events, she will mention something about her own life, such as what she was watching on TV, then feel embarrassed about oversharing.
This shows Nintendo's commitment to the development of Isabelle's character, as they could easily have Nook continue to read the announcements and leave Isabelle as a background character, but the player gets to interact with her daily and gets an insight into her personal life. With how frequent her roles have been over the past nine years since her introduction in New Leaf and being chosen for major outside appearances such as Super Smash Bros. Ultimate over Tom Nook, Nintendo is clearly going to push forward with more major Isabelle appearances in the future.