Dragonsbane

This book by Barbara Hambly came up once on Tim Ferriss in the episodes we index. That mention was a genuine on-air recommendation, not just a passing reference. The people who brought it up: Brandon Sanderson. Every occurrence below links to the episode page and to the exact second it was said on YouTube.

When the Black Dragon seized the Deep of Ylferdun, young Gareth braved the far Winterlands to find John Aversin, Dragonsbane -- the only living man ever to slay a dragon. In return for the promise of the King to send help to the Winterlands, Aversin agreed to attempt the nearly impossible feat again. With them, to guard them on the haunted trip south, went Jenny Waynest, a half-taught sorceress and mother of Aversin's sons. But at the decadent Court, nothing was as expected. Rebellion threatened the land. Zyerne, a sorceress of seemingly unlimited power, held the King under an evil spell, and he refused to see them.