Initiateur.
ETYM Latin: cf. French instigateur.
1. A person who initiates a course of action; SYN. initiator.
2. Someone who deliberately foments trouble; SYN. provoker, inciter, instigant, firebrand.
1. Someone who is an active supporter and advocate; SYN. booster, plugger.
2. A substance that in very small amounts is able to increase the activity of a catalyst