From A Wiki of Ice and Fire
Urrax was a dragon who may have lived in the time of the First Men.
According to legend, Serwyn of the Mirror Shield killed Urrax. Serwyn sneaked up on Urrax, hiding behind his shield which was a mirror, so the dragon only saw its reflection. Serwyn then killed him by plunging a spear though his eye.
A Dance with Dragons
When trying to get the measure of Tyrion Lannister, Haldon questions him as to how Serwyn of the Mirror Shield slew the dragon Urrax. He is unimpressed with Tyrion's correct answer, and asserts that even Rolly Duckfield knows that tale.
- ↑ 1.0 1.1 A Dance with Dragons, Chapter 8, Tyrion III.