Harald Karstark

Harald Karstark is a recurring character in the sixth season. He is played by Paul Rattray. After the execution of Lord Rickard Karstark by Robb Stark, Harald is the new head of House Karstark and Lord of Karhold. He is described as ruthless and calculating.

In the books
In the A Song of Ice and Fire novels, there is no "Harald Karstark" - the TV character is apparently a condensation of different Karstark characters from the books.

In the novels, Lord Rickard Karstark had three sons: his eldest son and heir Harrion was captured after the Battle of Duskendale, while his other two sons Torrhen and Eddard were killed in the war. Rickard also has a daughter named Alys. The TV series changed this around somewhat: instead of Torrhen and Eddard dying, it is stated - by name - that "Harrion" and "Torrhen" died, and no mention is made of Eddard Karstark - possibly to avoid the confusion of introducing another character named "Eddard" after Eddard Stark (though George R.R. Martin's entire point in reusing character names is because he thought it was contrived that there would be no repeated first names in an entire continent).

After Robb Stark executes Lord Rickard in the novels, the Karstark forces abandon him and return back to the North - and because Harrion is still a Lannister prisoner, Rickard's uncle Arnolf becomes acting head of House Karstark. Because the Karstark army did not remain in the south, it was not present at the Red Wedding to be destroyed along with the rest of the Northern army. This makes the Karstarks politically important in the post-Red Wedding North, as they are the only major Northern House (other than the Boltons) with their standing army still relatively intact - thus the Lannisters want to ensure that they maintain political leverage over them. Even after the Red Wedding, therefore, Rickard's surviving son and heir Harrion continues to be kept prisoner by the Lannisters - a tacit arrangement with Arnolf, who is much more willing to have House Karstark tolerate Bolton rule over the North when his new status as leader of his family is dependent on the Lannisters not releasing his great-nephew from captivity.

Arnolf is introduced in the fifth novel. He is not a lord but the castellan of Karhold. He is described as thin and twisted, one of his shoulders is much higher than the other. His eyes are grey and greedy, his teeth yellow, his forked beard a tangle of snow and silver. Only a few wisps of white hair still cling to his spotted skull. He wears a cloak of grey wool trimmed with black sable and fastened at the shoulder with a starburst wrought in beaten silver.