I am looking for a single-word English equivalent of "παράγων" as in "ο Τάδε είναι σημαντικός παράγων της οικονομικής ζωής του τόπου". I have searched in synonym dictionaries etc. but have not found anything satisfactory ("agent"? No.). "movers and shakers" is almost exactly the perfect equivalent but it's too informal for the type of text I'm working with, plus --unless I'm wrong-- we normally use it in the plural. (I suppose I could bypass this by saying "he is of of the movers and shakers... " but , as I said, it's too informal.). So, any thoughts?