Word for someone who thought of an idea
I think originator may convey the meaning:
- someone who creates new things
Also a conceiver or a mastermind according to context.
Source: www.thefreedictionary.com
I think that innovator is close to what you want
A person who develops a new design, product, etc. or who has new ideas about how to do something.
(source: oxforddictionaries.com)
For example:
"He was the innovator behind the revolutionary X software system."