Geoffrey is the possibly metafictitious hero of Felicity Beedle's seminal work, The World of Poo. He and his faithful puppy Widdler have what might demotically and accurately be described as a whole shitload of adventures in and around the city of Ankh-Morpork, a city once described by Sam Vimes as one where the streets are indeed paved with gold. Depending on how romantic or factual you are, that is, the streets are paved with fairy gold. Or at least that substance to which fairy gold characteristically reverts in the morning. The alternative is that the streets of the city are paved with the substance which Sir Harry King turns into gold.
Either way, Geoffrey, a young man with an inquiring mind, spends the 128 pages of the book getting right to the bottom of things, as it were.