[WP] You have a special ability: you live two lives. Whenever you go to sleep at night, your "dream" will be about your other life. Both lives you live are equally realistic and soon, you start to realize both lives actually take place in the same world, but centuries apart.
Ever since I have realized that both of my lives take place in the same world - I have decided to become god.
I have made it a habit to write journals, and keep them in a safe and secure place. That way, whenever I am in my future life, I can get my journals from the past, and read what will happen during the rest of my past life. Every time I lived my past life, I made adjustments based on what I've read, and that changed the text in my journals.
Given my ability to see my future in such extreme detail, plus my knowledge of the 21st century technology, it wasn't that hard to control a 3rd of the world by the time I was 25 years old.
Once I became a king, my goal was to rapidly advance technological progress, to create utopia for my future self. Since I could see the long term outcome of my every decision, I could steer the world in the right direction, and avoid all the major catastrophes and wars.
I was starting research projects in the 15th century, and my descendants worked on them for centuries, then, in 21st century I've just read the results, and quickly sent them back to my past self, thus eliminating the need for the project in the first place, and immediately getting answers to any question that I wanted. Any task that could be solved by the most powerful person in the world and his descendants in 6 centuries was solved by me in a day.
It took me 3 months to cure all the diseases, and extend the lifespan of a person to 400 years. Meanwhile, in the 21st century I was waking up every day in a dramatically changed and rapidly advancing world, because all the existing technologies were replicated by my past self, and then 6 centuries of technological progress were added on top of them.
Soon enough, I've managed to prolong my lifespan up to 800 years. The 15th century version of me was the empreror of the colonized sector of our galaxy, and 21th century of myself officially worked as his replacement.
Now my main goal was not to go crazy given the ridiculous amount of paradoxes this situation has introduced, while, as a side project, I was colonizing space, curing death, and developing the all-powerful AI that would help me to upload my consciousness into the computer.