Mind of a Genius

Genius is it a overrated word or really genius exist naturally, then how about Einstein, he was not the sharpest person in his class as a matter of fact he was sort of a dullard. And ultimately he came up with the theory of relativity which is widely regarded as the most important asset of our species. But how did this genius come about, did he "work" his way towards it or he was born with it. Is it an anomaly of that person or can a genius can be "built". I would appreciate a professional opinion, since people seem to be influenced by the movies and a fantasy that people associate with genius, ofcourse even I have been touched by it.

Believe in yourself.