So it turns out that Mark Gatiss is playing
Tycho Nestoris. That's the name of the emissary from the Iron Bank who reaches Stannis at the end of A Dance with Dragons
. I'd guess that Tycho will be combined with Noho Dimittis, the Iron Bank emissary Cersei sends away in Feast
-- I had forgotten they were separate characters. It may be that the Iron Bank strand is being emphasized earlier on the show than in the books, or that an awful lot of Feast
material is in the latter half of season four.