GRRM has teased us with another Froggy casting clue as follows...
"Once more into the breach....
Vengeance is his. Frankenstein and Nessie are friends of his, but don't say he's never been human... but was he Irish or Eskimo? Born in Scotland, that we know. He's been a fisherman, a minister, an inspector, and a malingerer. Down the slippery slope he slides, toward the kingdom of bones, but will he lose his head?"
Source: Not-A-Blog
I came into this one late and it seems as if Winter-is-Coming has the case cracked.
The actor appears to be John Stahl and the role could very well be Lord Rickard Karstark.
-"Frankenstein is a friend of his" = he portrayed Ewan in Frankenstein on National Theatre Live.
-"Nessie is a friend of his" = he was in movie called Loch Ness.
-"but don't say he's never been human..." = he was Quinn on Being Human.
-He was First Fisherman in Loch Ness.
-He was a Reverend (Minister) on Rebus.
-He played Inspector Reed in Resort to Murder.
-He was in an episode of The Tales of Para Handy called The Malingerer.
-"Down the slippery slope he slides" = he was in an episode of Doctors called Slippery Slope.
-"the kingdom of bones" = an episode of Murder Rooms he was in.
-"Vengeance is his" and "will he lose his head?" point towards Lord Rickard Karstark.
*UPDATE**
George confirmed John Stahl as Lord Karstark on his blog.
"Thanks for playing, everyone.
Some of you got it. Some of you didn't.
It's actor JOHN STAHL.
He will be portraying one of Robb Stark's bannermen, Lord Rickard Karstark.
The major roles for season two of GAME OF THRONES have all been filled, but casting continues in London, Belfast, and Dublin for various smaller parts."
Source: NotABlog
Streaming Options