Ventriloquist

The villain known as "the Ventriloquist" is a fairly ordinary man named Arnold Wesker. He is constantly accompanied by his ventriloquist's dummy, Scarface, which is modelled after the gangsters of the 1920's. Scarface speaks and acts with a completely different personality from Wesker himself; the Ventriloquist's thugs and underlings are convinced of this to the point where they refer to the puppet as their boss and speak directly to it while giving reports or asking for orders. Scarface is often equipped with firearms built in miniature to fit his undersized hands, but which fire real, perfectly lethal ammunition.
 
The exact depictions of the character have varied; sometimes, Wesker is depicted as a meek victim, helplessly going along with the malevolent will of Scarface, and sometimes it is clear that he merely uses Scarface as a surrogate for his own plans for crime and destruction. Equally unclear is the exact nature of Scarface; in some depictions it is stated that Scarface is an alternate personality of Wesker's that only manifests while he is holding the dummy, and sometimes the dummy seems to literally have a life of its own. 
 
Batman's clashes with the Ventriloquist traditionally end with the Scarface dummy either being destroyed or forcefully removed from its owner, at which point Wesker finds himself frozen with uncertainty, unsure of what to do, and is quickly apprehended. But no matter how many times Scarface is destroyed or taken away from Wesker, they always end up together again. Several times Wesker has seemed cured of his psychological issues, only for the dummy to inexplicably show up in his home, leading to a new crime spree, and just as many times Wesker has carved a new Scarface out of any available wood.
 
The Ventriloquist himself did not make an appearance in Batman: Arkham Asylum, but a biography of the character could be unlocked by scanning a tommy gun with his name displayed on a plaque beneath it. In addition, Scarface did appear, and in addition to having a separate biography from Wesker (obtained by scanning the dummy itself), Scarface appeared in a single cutscene, held by the Joker, in which he spoke in a manner very unlike that of the clown prince of crime, going so far as to insult the Joker to his face. This could suggest that Scarface does have a mind of his own, which only manifests while he is being held... but then again it is equally possible that the Joker was simply amusing himself by mocking his fellow villain.