In group decision-making contexts, what are the five potential individual roles involved in the purchasing decision?

Initiator: The person who brings up the idea or identifies a need.
Gatekeeper: The person who conducts the information search and controls the flow of information available to the group. In organizational contexts, the gatekeeper identifies possible vendors and products for the rest of the group to consider.
Influencer: The person who tries to sway the outcome of the decision. Some people may be more motivated than others to get involved, and participants also possess different amounts of power to get their point across.
Buyer: The person who actually makes the purchase. The buyer may or may not actually use the product.
User: The person who actually consumes the product or service.