Synonyms genius (someone with great mental ability): He is a genius at mathematics.
John was a great genius. prodigy (a child having extraordinary talent):
She was an infant prodigy, composing music at the age of five.
brain (a highly intelligent person): He is in fact one of the best brains in this country.
The best brains in this country are working on this problem this time.
mastermind (someone who plans and organizes):
He was the mastermind behind the bank and also jewelry robbery.
He is also the mastermind behind a huge drug-smuggling.