Leonardo Da Vinci?
I dunno what to think of Leo D. anymore. Either he's supremely genius, or he's terrifyingly genius. He's not only a drawer. He's the frontrunner of an era that if anyone heed his wisdom, the world would change dramatically.
Like in Assassin's Creed II and Assassin's Creed: Brotherhood, he reinvented Altaïr's (possibly trademark-able) Hidden Blade, with poison and mini-pistol upgrades (which was first invented by Altaïr himself), with old pages from 300 years ago! Then he invented the bloody flying machine. A flying machine! I know that was only a glider from today's view, but guys, that was bloody 600 years ago! Brothers Wright didn't invent their first aeroplane until 1903. That was about 500 years later!
Leo's glider need hot air to maintain altitude and speed, that was a bit old-fashioned, but back then there was no aerodynamics or whatever we learn today. And still his glider flew across the night sky.
And if Altaïr's blade was fiction, the war machines in AC:Brotherhood were not. There were historical facts that the blueprints were drawn for tanks (mobile heavy cannons), combat airplanes (actively fire weapons to attack and maintain altitude and speed), light machine guns (quick fire bullets with less durations), and fast-action battleships (smaller in scale to increase speed yet without costing any firepower). Each of them was not mass produced, yet will change the world if they were. I guess he would never know that those weird drawings he drew on scraps of papers would become the standard equipment of modern militaries a few centuries later.
During the Renaissance, people don't pay attention to Leo, yet he managed to put a dent in the universe with a few scratches on papers. Hundreds of years later, we opened our minds and acknowledged Leo's achievements, yet he is no more. Leo literally changed the world back then when everyone thought the world was flat. Imagine how much of our world he would change if he is living in our time, right here, right now, in the 21st Century.