The Chairmouse is shown to be in a leadership position alongside him being very determined to save and is shown to be loyal to his case, allowing though reluctantly Miss Bianca to go and save Penny. He is also shown in the beginning to be disdainful (and also rather blunt) to Bernard (him being a janitor) to go alongside Bianca on the quest, though he is allowed.
The Chairmouse is shown as a larger mouse, with larger ears and longer fingers. He is shown to be pompous with dark crème skin and pinker ears within. He is shown to also wear a blue and indigo (with white tips) suit alongside a monocle when needed.
The Chairmouse is the head of the International Rescue Aid Society located in New York City. At the beginning of the film, he calls for an emergency meeting because he believes to have received a call for help. After opening the meeting, he has Mouse Scouts bring in a large bottle, which was found in a nearby river. The Chairmouse asks Bernard, the janitor, to retrieve the note that is in the bottle. The Chairmouse discovers that the note is addressed to Morningside Orphanage, an orphanage located in New York. The note is watered out, leaving the Chairmouse unable to decipher it. However, Miss Bianca is able to discover that the note is from a girl named Penny, who is apparently in trouble. Out of compassion for the girl, Miss Bianca asks the Chairmouse to give her the assignment. The Chairmouse agrees, but only if Miss Bianca chooses a male co-agent for safety. Miss Bianca chooses Bernard, and after they leave, the Chairmouse makes a remark about the fact that a lady and a janitor have taken on the assignment.
The Chairmouse reappears at the end of the film though without any lines (only heard in laughter) when the delegates are watching a news program detailing Penny's fate. He is seen to laugh when Penny mentions that she was helped by talking mice. Suddenly, Evinrude arrives from the bayou with a note for help. The Chairmouse sends Bernard and Bianca on the assignment after Bianca volunteers the two of them alongside Evinrude.
The Chairmouse returns for the sequel, with a similar role and also with Bernard Fox reprising his role. He is first seen holding another meeting in the middle of winter with it also being night so many of the attendees are nearly asleep with him encouraging them. He reveals that a distress signal has been sent revealing that a boy has been kidnapped in Australia He decides that their two best agents, Bianca and Bernard, should be sent (with no one disagreeing), but he is shocked to discover they are absent, having been on a date in a fancy restaurant where Bernard secretly intended to ask Bianca to be his bride. When Bernard and Bianca arrive, the Chairmouse briefs them on the mission, which they accept (Bianca more than Bernard). The Chairmouse shakes their hands and tells them that, despite the heavy snow, they must leave immediately. Unlike the first film, he does not make an appearance for the rest of the film.
In the sequel, the Charimouse returns with Bernard Fox reprising his role, with him (alongside Miss Bianca and Bernard) are the only characters returning from the original film
Bernard Fox, who voiced him also voices Dr. Mouse in the sequel