Past. Given that I and the people of the past can understand each other, It wouldn't be extremely difficult to make myself a king simply by distributing knowledge that the real geniuses were to late to invent; they didn't have my advantage. Before travelling, I'd study the greatest inventions: the printing press, the aircraft, the transistor and the like. When I knew them, I'd go back, and use these inventions to make myself be called a genius. I'd use the powers granted by my stolen science to make myself an empire literal centuries ahead of its time. I'd take control, and live happy being king of the world. Yes, I'm arrogant enough to think that I'm capable of doing all this.
Albeit, time travel is hard. It's all just a fantasy.
