Who is the smartest human being that's ever lived?

Salman Khan. In 1998 at MIT, Sal achieved three BSc degrees in mathematics, electrical engineering, and computer science whereafter he completed two MSc degrees in electrical engineering and computer science. He also holds an MBA from Harvard. He left his job as a hedge fund analyst after discovering educating millions of people—through his paragon teaching style—was in the realm of possibilities.
I believe the smartest people who roam the universe are simultaneously the most unpretentious because through hindsight they realise it is not inherent intelligence, but persistent passionate diligence, curiosity, and a willingness to grow that's key. They also took notice that the environment where kids grow up, which makes or breaks curiosity, is entirely up to chance; and an unfavourable one at that.
That being said, Sal chose sharing wisdom over utilizing it for lucrative intentions. And judging from his various degrees, the latter possibilities could've been endless. To this day Khan Academy has offered a helping hand to over 40 million people worldwide, for free!
His genuinely compassionate and charismatic approach has impacted and will continue to impact millions of lives. Team Khan Academy is closing the illusionary gap between the layman and the wonderful Shangri-La that is science. Ultimately leveling up our humanity. Sapere aude!
PS Obviously John von Neumann and Leonhard Euler were among the true geniuses, but I felt this message was important enough because too much human potential is wasted by a predominantly archaic education system.

Which is more important, the study of physics or philosophy?

All of life’s experiences are shaped by our mind. Philosophy seeks to answer what is a good life; a healthy mind. Therefore, mastery of numbers and equations is in vain if the physicist does not know how to live. Does he live for the sake of progress and productivity? Or does he live for the sake of curiosity. Is he just living? Or does he feel alive. When philosophy dies, humanity dies with it.
Former Quora answers; before deleting my account.