I love this idea - it needs to be a long-running TV series.

Modern high functioning genius who is part Da Vinci, part MacGyver, and part Dr. House, gets blasted back to BFE in the stone age while conducting experiments that he started because he was fixing something broken by our society (war, starvation, environmental disaster, superbugs, whatever).

Once he gets his bearings in the new world (I'm assuming "he" because it makes the story a little easier to tell, but gender bending this might be pretty entertaining, too, especially if our heroine also had some mad combat skills to pull out every once in a while), he says fuck it - I'm going to reshape the world into a better place than the one I left.

Parallel earth is born, and we have all kinds of fun dramatic tensions to play out.

• Butterfly Effect meets pre-destination.
  
• Kindness meets savagery.
  
• Supersition meets reason.
  
• How do you stay human and hopeful the more savagery you see, and the more distant you get from the people you are trying to "save"?
  
• When do you become wise enough to realize you cannot "judge" others? And when do you realize that you have to act?
• How do you deal with love in a culture?
• How do you deal with love of people you will outlive
• How do you escape persecution when people realize your differences (longevity, intelligence, different mores)
• Every tool is a weapon, and every weapon is a tool. How do you even see the impacts of your actions? For instance, fire protects, but fire kills.
  
• How do you preserve anything over time and vast spaces when there is no settled economy, infrastructure, etc.?
  
• How do you draw the line between pragmatism and idealism when you know people will die (and you'd totally blow your cover by pulling all the stops out to save them)
• How do you teach values that are basically magic to others? For example, how to teach hygiene to people who do not understand germs?

The possibilities are literally endless.