Physical appearances had almost no say. Had they more input, he wouldn't have been the slightest bit terrifying. Well groomed, dark hair, neutral features; even after centuries, his ears had only taken on a slight point, and being a human by birth, he had no other elven features, despite being a Rider. The one exception was his eyes, with beetle-black irises. One could drown in their depths, with miles worth of layers of differing shades of black, and there reached a point where no light would have any hope of ever coming close to reaching - the deepest furrow in the deepest trench in the deepest floor of the ocean.
But one could look away from the eyes, so long as they were unbound by all means, magic and otherwise. Yet any standing near would find it impossible to escape his presence, his overpowering were many factors, some greater than others: the astounding sense of superiority he beheld was one, and not even the worst of them at that. Any and all of his subjects were well aware of his power. This went far beyond mere reputation. One would always be aware that he could do anything he pleased with them. Brush past any mental barriers they may have founded with ease. Kill them with a word. There was no evading him. And it wasn't even necessary for these thought processes to come to mind for one to be aware of his nature. As soon as one set foot in the same room as him, they would know, weather they were fit as an ox or both blind and deaf. As thoroughly as one might attempt to convince themselves otherwise, even those who worked for him, who viewed him in benevolent light, would always be aware they were nothing before him, and the only thing holding back his wrath would be his need for them, or their own self not being a threat. As soon as this changed, he would snuff them out like a candle, and they could do nothing. They all knew this, from the first glance, from the first taste of the air that hung over him. They were nothing. He had experienced things they had never dreamed of imagining. Suffered losses they couldn't begin to fathom, been given gifts they did not know existed. He had worked up to his current position by centuries of work, gaining power, losses and victories in turn. They were nothing. And he was Galbatorix.
Manipulation. Another one of the many powers he possessed. This made everything worse by tenfold. He could suck you in. It wouldn't have been so bad if his voice matched his air, wary and powerful,(and to some individuals, just plane evil), but that was often not the case. Manipulation. In reality, he had the ability to make his voice sound rich and intoxicating. Smooth, confident, but not giving anything away. Manipulation.
Hint hint: The safety word is: Jarnunvösk