King Clarkson might be the boss 'round these parts, but he's not exactly the most charming guy in the world. Sure, he seems smart and is obviously a capable ruler, but he lacks the empathetic nature that makes Maxon and Queen Amberly beloved by everyone they meet.
In fact, King Clarkson and Queen Amberly are often contrasted with one another. Queen Amberly clearly plays the comforting role in the family, while King Clarkson is more of the disciplinarian. But we also see the difference in how each character approaches politics. For example, when Maxon announces his food assistance program, his parents have wildly different reactions: "the queen was radiant with pride" while "the king was clapping but without excitement" (18.97).
Actually, King Clarkson seems to get tense whenever Maxon asserts his authority. Is that because the King feels threatened by his rising son? Or does he genuinely disagree with Maxon's idealistic plans for saving Illéa? We're not sure, but either way, their interactions give us a sneaking suspicion that there's something sour going on with the cranky King Clarkson.