Alright, so the obvious physical resemblance speaks for itself here: they're both bald(ish) men who aren't exactly skinny, but what else? Varys is a eunuch and Heyman has never really had any on-air romantic involvements to speak of. Then there's the fact that they're both among the greatest speakers in their field: Heyman's mic skills are out of this world, and Varys uses his tongue for the purpose of mass manipulation with the help of his "little birds". They're both extremely intelligent and have their fingers firmly on the pulse: they're respected as such even by their enemies, because these are two smart cookies you do not want to cross.