Mr Gryle was a banshee who made his appearance in the novel, Going Postal. He appeared to be wearing a thick leathery cape, but that was really his wings tightly wrapped around him. The muscles in his chest were immensely tough, protecting as they do both his hearts. An extremely unlikeable character, he told Stanley Howler that he "gnawed his grandmother's bones". He had very few needs in life, but he did have a passion for pigeons, not the best passion in Ankh-Morpork where the pigeons are particularly toxic, "dogturd burgers".
In earlier novels, the reader had been told that Mr.Ixolite, who is a member of Reg Shoe's Fresh Start Club was the Disc's last surviving banshee but perhaps Pratchett was referring to "civilized banshees' rather than feral ones. Clearly Mr. Gryle was a feral one as he was a ruthless killer who worked for Reacher Gilt, the evil Chairman of the Board of the Grand Trunk Clacks network. Mr. Gryle was the ideal assassin because he could arrive by air and leave few clues for anyone in the Watch to decipher, as well as having little tangible smell for a werewolf like Angua to identify. He was responsible for the death of John Dearheart at the beginning of the novel who Reacher Gilt wanted disposed of because he was starting a rival Clacks system. He murdered Reacher Gilt's fellow Board member Crispin Horsefry when Crispin begins to panic and get cold feet about the Grand Trunk's business practices. He was then hired to destroy the Ankh-Morpork Post Office and assassinate the Postmaster Moist von Lipwig. However, he was only given a vague description and assumed the man wearing the Postmaster's hat must be Moist when in fact it was Acting Postmaster Tolliver Groat instead. He was foiled in his murderous attempt by Stanley Howler who, when confronted by Gryle, had one of his "Little Moments", and hit Gryle in the mouth with a sack of pins. Gryle retreated into the Sorting Office after setting fire to the Post Office., where he and Moist von Lipwig had a final showdown - Moist helping get Tolliver Groat out of the burning building and then, in hero fashion, returning to rescue Mr. Tiddles, the Post Office cat. The two battled in the Sorting Room, Moist stabbing Mr Gryle but missing both his hearts. In typical banshee fashion, Mr Gryle screamed to indicate Moist was about to die (ie be killed by him) but Moist had been raised in Uberwald and knowing he had to get inside Gryle's defenses, stepped forward and shoved Mr Gryle into the Sorting Machine designed by Bloody Stupid Johnson, causing the banshee to be scattered across space and well and truly sorted.