Koschei - The Master - looked down upon his planet with glee. He had spotted it in one of its early stages, barely enough science to power a small light. Much was still consumed by the wild unknown. In a way, he had pitied the planet. But there was another feeling he had, something all Time Lords have an unofficial sense of. He saw the planet's potential.
He knew he needed to guide this planet. They would thank him - call him a god, if he did his mission well enough. The Master set to work. He went back to when the yellow, four-eyed humanoids knew only to live, and that they must die. In other words, when they were primitive life forms hardly evolved from monkey-like creatures. He gave them fire, and tools. And before they could thank him properly with their grunts they used as language, he left for the future.
In order to avoid a paradox, the Master reappeared on the planet just after he had originally seen it. All was as it should be. They had electric lights, nothing else. Something different, or perhaps that he should not have seen from space, was that there were legends of The Fire-Bringer. He smirked, keeping his black hood low over his face. At first, he struggled to think of what to do. Then he remembered what he had learned in the Year That Never Was. These beings were so like humans, it would be no shock that they thought like them as well. He needed to keep them in the dark, of everything. He would lead them to salvation, and they would thank him, and revere him. He smiled just thinking about it.
After finding the leader of this small planet with some difficulty, he informed him - Filluzlek - that the Fire-Bringer had returned, with more gifts. The Master looked over at a plant in the room he and Filluzlek were in. With a flick of the Laser Screwdriver, the plant caught fire. Filluzlek bowed with respect and slight horror, before running off to spread the news of the planet's most well-known god, without saying a word.
And even after many years of hard work, sending the humanoids into mines, forests, and even the ocean to find the materials that the Fire-Bringer promised were necessary for the next project he would give the builders and scientists, that they were still content.
The one problem The Master spotted, but didn't care to pay much attention to, was the fact that his entire plan was based around the naive hope of these beings. They /hoped/ he would give them the next project to better their society, they /hoped/ he was telling the truth about his sacredness, they /hoped/ that if they mined enough resources, they would have their wondrous city that would be the envy of all other civilizations. The Master knew of course that he would give them what they wanted so badly. He had the plans for many things, such as single-person flying machines he had drawn up when bored, but it would take a very long time before he was willing to give them up.
There was, of course, a reason The Master was doing this. There was the feeling of power, of knowing something depends on you to guide it through the darkness, so it doesn't sit there sucking its thumb all day. Then there was the feeling of almost insane teasing. He could promise he would send plans for generations if he wanted to, though he suspected this was not a good idea - They would catch on eventually. The Master almost loved that it was this easy. All he had to do was something nice for the planet in its early stage, and then he could make it into his own architectural experiment that he could control by casually mentioning his Almighty Will to someone.
Once again, he looked down from his balcony in his palace by the sea at the hundreds of workers hauling stone from the quarry and wood from the forests. He thought of how much he had done for this planet. It was right they would thank him, and make him their king. He had given them light, and survival, and civilization. He deserved this. But there was a sound. At first, he thought he was imagining it, but after a moment, he looked around, and he knew that he was not. It was the unmistakable sound of a TARDIS with its brakes left on. The blue box materialized. Just like that, The Master's face fell, and as he knew too well, so did his time as rightful King.
The Doctor ruined everything.