Grant has appeared in several shows including, Doctor Who and Girls, and had memorable turns in Spice World and Hudson Hawk. But is perhaps best beloved by cult movie fans for Withnail and I, which also starred Eighth Doctor Paul McGann.
He was also, very briefly, cast as the Doctor for a series of flash-animated episodes on the official Doctor Who website in 2003, but this was cut short when the new series went into development.
It is unclear who he will play, but Watchers on the Wall suggest he might be Randyll Tarly, the as-of-yet uncast father of Samwell Tarly or a member of a theater company they’ve heard will make an impact on the show’s sixth year. It is also possible he may play Aeron Greyjoy, Theon’s uncle and a priest known as the Damphair.
UPDATE: Variety has confirmed Grant will be on the show, but his role is still “undisclosed.”