Role in the series
Basil is a take-off of the classic Sherlock Holmes character, modeling his career after the famous detective's. Basil is portrayed as a brilliant, plucky mouse who refuses to back down or end his pursuit against Prof. Ratigan, which makes him tenacious. Basil comes off as a jack-of-all-trades at several points in the movie, showing skill in areas such as science, history, and disguise (though his disguise inevitably fails), not to mention being physically capable (this is emphasized in the film's climax in the Big Ben Tower).
Despite this, Basil can also be prickly and self-centered, ignoring Olivia and Dawson at the beginning of the movie, and only offering to help them once he realizes Olivia's case might be the solution to finally capturing Ratigan. Though Basil is always calm and collected during his hunt, he can also be very emotional and operatic, becoming very moody if things do not go his way or if the situation looks dire, such as in the beginning of the movie and when he is nearly defeated by Ratigan. Despite his indifferent attitude towards Dawson and Olivia, he can be quite affectionate, as shown when he tries to cheer up the former after losing Fidget in the Toy Store, and also when he admits that Olivia is 'not such a bad girl'.