Leonard of Quirm is a fictional character in the Discworld novels by Terry Pratchett. He is a pastiche on the popular perception of Leonardo da Vinci.

Leonard is a man of indeterminate age. Originally from Quirm, he moved to Ankh-Morpork a long time ago and is currently a permanent guest of the Patrician. Before this he was a member of nearly every craftsman's Guild in the city, most commonly being kicked out for getting impossible high marks on examinations or correcting the questions.

Like his counterpart, he is a great painter, being known for such paintings as Woman Holding Ferret and the Mona Ogg. (Leonardo's Lady with Ermine and Mona Lisa.)

He is also a brilliant engineer. Like the early Leonardo he has designed a great number of war machines, and like the later Leonardo he holds war to be the worst of human activities. It has been noted, however, that the sketches which he makes of the devices he imagines variously show '. . . numbered parts and a list of instructions . . . ' or '. . . practically include glue and transfers'. Still others have noted that the sketches deal with the swift removal of inconveniently placed mountains, or show dying sailors leaping from burning ships into a boiling sea.

Despite this, Leonard views all his martial designs as intellectual exercises, and refuses to believe anyone would be mad enough to make them. It is this naïveté that has led to his imprisonment by the Patrician, lest someone other than him make use of the man's genius. But as long as he has paper to sketch on, and can watch the birds, Leonard barely notices his imprisonment.

He has also designed many less dangerous devices, including a submarine (The Going Under The Water Safely Device), an Espresso machine (The Very Fast Coffee Machine) and a coding machine (the Engine for the Neutralizing of Information by the Generation of Miasmic Alphabets, see Enigma machine). His genius doesn't quite extend to names. He also finds it impossible to focus on anything. Or rather, he's focused on everything, all the time. Many of his inventions started out as something completely different, before his mind shifted tracks half way through.

Again, like Leonardo, one of his greatest ambitions has been to build a working flying machine, something he achieves in The Last Hero.