I am looking for the exact term for the man who made a difference. Any help would be much appreciated. Thanks!
Idiomatically, people like this are called...
Movers and shakers - People of energetic demeanour, who initiate change and influence events.
For an adjectival form, it's common to say they're influential people (people of influence).
As @user3169 commented, there could be many depending on context, but you could consider using game changer which means:
a person or thing that dramatically changes the course, strategy, character, etc., of something