I have this crackpot theory (that's for you to decide) that Jaqen H'ghar is really Gerion Lannister. Let me explain why before you start cursing me.
The Valyrian steel greatsword of House Lannister, Brightroar was lost with Tommen II Lannister when he sailed to the Smoking Sea, to find riches, plunder and the remaining sorcery in the ruins of Valyria, a century after the Doom. The fleet, Tommen and Brightroar never neturned.
Now fast forward to 291 A.C. when Gerion Lannister, Tywin's y