Cox talked a little about his experience with Tolkien and the folklore the author often used as inspiration.
Brian Cox Talks Succession, The War of the Rohirrim, and His History and Experience with Tolkien
When you cast someone like Brian Cox as your king, you know what you're getting into, and Cox delivers in The Lord of the Rings: The War of the Rohirrim as the reknown Helm Hammerhand. If that name sounds familiar to you, that's because the notable fortress known as the Hornburg in Middle-earth was known as Helm's Deep, thanks to the events that occurred in War of the Rohirrim. The film tells the story of a legendary king of Rohan who was forced to defend his kingdom against an army of Dunlendings.
In Tolkien lore, the Dunlendings were wild men who lived near Rohan and often got into conflicts and altercations with the Rohirrim. In the movie, Wulf (Luke Pasqualino) seeks vengeance against Cox's Helm Hammerhand after Helm rejects the offer Wulf's father makes to marry his son to Helm's daughter, Héra (Gaia Wise). This begins a feud that leads to bloodshed and death and forever changes Rohan.
Collider spoke with Cox about playing Helm Hammerhand and the actor's history with Lord of th