Constable Visit-The-Infidel-With-Explanatory-Pamphlets was a member of the Ankh-Morpork City Watch of Omnian faith. His fanatical preaching and evangelism led to a great fear of him among heavy drinkers, who would play dead should he walk by the pub they're drinking at.
He takes a dim view of other religions, calling any references to anything religious not related to Om as "misguided" and "false".
His behaviour is similar to door to door evangelism famously used by religious missionary groups such as Jehovah's Witnesses or Mormons. It is stated in Feet of Clay that during his time off, he and his friend Smite-the-Unbeliever-with-Cunning-Arguments do go door to door.