Cley Cerwyn

"Lord Cerwyn refused to pay. He said the Warden of the North would always be a Stark, and he’d be damned if he’d kiss a traitor’s boot...I flayed him living, along with his wife and brother. Made his son watch...The new Lord Cerwyn paid his taxes."

- Ramsay Bolton

Cley Cerwyn is a northern lord and the new head of House Cerwyn

Season 5
Roose Bolton sends his recently legitimized bastard son Ramsay to Cerwyn to collect taxes from his new vassals. Medger Cerwyn, however, refuses to pay, proudly professing his loyalty to House Stark and denouncing Bolton as a turncoat. For his defiance, Ramsay has Medger flayed alive, along with his wife and brother, all the while forcing his son to watch the ordeal. When Ramsay relays these events to his father he casually remarks that the new Lord Cerwyn paid his taxes.

Season 6
Cley Cerwyn, as the Lord of House Cerwyn, joins the other Northern Lords gathered in Winterfell after the Battle of the Bastards. After being chastised by Lyanna Mormont for not aiding Jon Snow against Ramsay Bolton, who flayed his family alive, a repentant Lord Cerwyn declares Jon Snow King in the North.

In the books
In the A Song of Ice and Fire novels, Cley is the son of Lord Medger Crewyn, who died of wounds he took at the Battle of the Green Fork.

While Ramsay Bolton did not kill Medger in the novels, he did kill his son Cley Cerwyn, at the Sack of Winterfell. When Rodrik Cassel hastily assembled a force to besiege Theon Greyjoy in Winterfell, composed of about 2,000 men from the few household soldiers left in the North, 300 of them were Cerwyn men led by Cley. Ramsay then arrived with 600 Bolton men, whom Rodrik and his lieutenants welcomed as their allies - but as soon as they were in the camp Ramsay's men betrayed the other Northern bannermen in a surprise attack, taking them totally off-guard. When Rodrik walked up to greet Ramsay by extending his hand in friendship, Ramsay quickly drew his sword and cut off Rodrik's outstretched arm at the elbow. Cley Cerwyn was killed in the betrayal by an arrow to the eye.

After Cley's death, Jonelle Cerwyn, his elder sister becomes the Lady of Cerwyn. Like the show version of Cley, she begrudginly swears allegiance to House Bolton.