If you need to talk to a rogue nation and traditional diplomats just won't do, then Bill Richardson is your man. Yesterday, he met with the President of Cuba's parliament to discuss trade issues. Shortly before that, he met with North Korean diplomats after the release of Laura Line and Euna Lee, acting as a representative of the Obama administration. His history schmoozing with global pariahs, in fact, goes on and on, as this 1997 TNR piece by Jacob Heilbrunn proves.
It's worth reading the whole thing (along with Ryan Lizza's classic Richardson profile).