  Disorder, ubiquitously present in solids, is normally detrimental to the
stability of ordered states of matter. In this letter we demonstrate that not
only is the physics of a strong topological insulator robust to disorder but,
remarkably, under certain conditions disorder can become fundamentally
responsible for its existence. We show that disorder, when sufficiently strong,
can transform an ordinary metal with strong spin-orbit coupling into a strong
topological `Anderson' insulator, a new topological phase of quantum matter in
three dimensions.
