Every man going on secret missions to save the world needs a gadget man. Even if you live on a flat world and you belong to The Monks of History (the most secret society that never existed). Just as James Bond had Q, (and now has R) for the most complex cell phones and watches, like Spyfox has Quack for a few odder gadgets, Lu-Tze has Qu for exploding mandalas, killer prayer drums (in an emergency you can even pray with it), and begging bowls with hidden blades. But his crowning achievement is his portable procrastinator, which allows the wearer to carry a little bit of stored time with him, just in case time stops (this is a recurring problem on the Discworld). It's still being improved, as are many of Qu's gadgets. Currently, its chief problem is the fact that it runs on clockwork.
Qu is another example of Terry Pratchett's marvelous ability to take something to its ultimate satirical conclusion. It would be enough to just have Lu-Tze, the seemingly simple monk who is really a secret operative, but no. We have to go the whole hog and give him all the trappings of a secret agent.