Initiator (noun)

1. A person who starts or initiates something.
2. The person who takes the first step in a process or action.

Origin:

From latin initiator (a beginner, an introducer), from initiare (to begin, to initiate).

Examples:

1. He was the initiator of the project.
2. She was the initiator of the movement.
3. The initiator of the company was the one who had the idea.
4. The initiator of the plan was the one who proposed it.
5. The initiator of the revolution was the one who sparked it.