What is the hound in Fahrenheit 451?

The Mechanical Hound, similar to contemporary firehalls, is the mascot. In the world of Fahrenheit 451, however, the traditional, firehall dog has been replaced with the predatory, murderous Mechanical Hound, which can be programmed to pursue any target desired. The Hound in Montag's firehall is programmed to pursue Montag himself, although the Hound is eventually destroyed by Montag. Another Hound, similarly programmed, is set after Montag when he is discovered to have had books in his possession, but is fooled by him when he takes refuge in a river.