1. influential person or aspect, means by which something happens
driving force behind idea/industry/company
This expression takes its meaning from the ability of an engine to provide the necessary force to move a vehicle. 'A driving force' is someone or something that has the power, energy, or impetus to make things happen, or somebody with the ability to motivate or influence others to get things done. It is almost always used in a positive sense, and often used in a professional context.