Let me just get this out there—that's a tricky one. 'Hobbit Orc King' isn't the title of a specific, mainstream Tolkien novel. It sounds more like it could be a fanfic descriptor, maybe a phrase someone would use to search for the character Azog the Defiler from 'The Hobbit' films? Or perhaps it refers to some video game or indie novel riffing on the concept. Azog is the big antagonist, that pale orc who swears vengeance on Thorin's line. In the book 'The Hobbit' itself, the orc leader is more generically the Great Goblin, who dies in the Misty Mountains. So the 'Orc King' as a major player is mostly a Peter Jackson invention.
If we're talking about Jackson's movies, the Orc King—Azog—plays the role of the persistent hunter. He's the physical embodiment of the vengeful past haunting Thorin, a narrative device to keep the pressure on the Company outside of Smaug. He’s not in the original book at all, so his role is entirely to externalize Thorin's inner conflict and provide more action set pieces. Honestly, I found him a bit of a one-note, CGI-heavy threat compared to the more nuanced villains in Tolkien's writing. The movies needed a face for the orcish hordes, and he's it, but he doesn't have much depth beyond 'murderous rage.'
It's interesting how adaptations add elements like that. It makes you wonder if the role is less about the orc king himself and more about what he represents for the hero's journey. For Thorin, Azog is a ghost from a past battle, a reminder of legacy and loss that has to be confronted before he can claim his home. Without that, the story might feel like it's missing a consistent external threat until Smaug shows up.