What is the name of the villain in The Great Mouse Detective?

The villain in The Great Mouse Detective is Professor Ratigan.

Ratigan is a criminal mastermind and Basil of Baker Street’s chief nemesis in Disney’s 1986 animated mystery. He kidnaps the toymaker Mr. Flaversham and forces him to build a clockwork replica of the Mouse Queen, planning to overthrow her and become the ruler of all Mousedom.

Although Ratigan is a rat, he despises being reminded of that fact and insists on presenting himself as a refined genius. Vincent Price supplied his voice, giving the villain a theatrical, sophisticated menace. His principal henchman is Fidget, a bat with a crippled wing; Dawson is Basil’s friend and investigative partner, while Basil himself is the heroic mouse detective.

The story is deliberately modeled on Sherlock Holmes. Basil lives on London’s Baker Street, takes his name from actor Basil Rathbone, and even shares the film with Rathbone’s archival voice as Sherlock Holmes. The climax sends Basil and Ratigan into Big Ben, where their final struggle ends with Ratigan falling to his death as the clock strikes 10.