The Rincewind Trilogy(2001)

Terry Pratchett

On a flat alternate reality, scruffy-bearded Rincewind, sixteen years at the lowest level of the Unseen University, silver letters on his droopy-brim pointed hat spell WIZZARD, and his robes of faded red, are the only proof of his profession. The harder he runs from trouble, the deeper he gets entangled.
1 Sourcery 1988 is natural magic from Coin, the eighth son of the eighth son of the - you get it. His powerful papa-possessed staff jolts the lazy gluttonous professors against the wishes of the late ArchChancellor's determined talking hat.
2 Eric 1990 is a rude acne-pimpled boy who summons Rincewind instead of a demon to fulfill his wishes of riches and womanly partner in sort-of Aztec Mexico and Troy.
3 Interesting Times 1994, like the Chinese curse, sends Rincewind to the Aurient where Ghengiz Cohen and the white-haired hobbling heroic Silver Horde of seven conquer villainous Vizier Hong with rumors of a ghost army and terra-cotta tomb soldiers.