The Nobili's were once a respected crime family, who were down on their luck and had a tarnished reputation thanks to other similar families. Gordon and his two sons, Carmen and Joey, were all that remained of the family. All three were exposed to the Mists, however the sons were both killed by the Thunderbolts. As the last of the Nobili line, Gordon's power is that every single one of his ancestors is able to manifest themselves upon him, and from them he can draw all of their memories and knowledge. This means that he could well possess knowledge to an awful lot of secrets and information, which if used for the wrong reasons (as you'd suspect it would be) would make him a natural target of S.H.I.E.L.D. After all, if they going to be introducing more Inhumans as good guys, it makes sense to bring in a few bad ones to balance the sides.