key decision-maker - это основное лицо, принимающее решения
или это лицо, принимающее ключевые/основные решения

Спасибо!

http://www.users.cloud9.net/~kvivian/html/decision_makers.html
In the proposal process different people play key roles at different points of the decision making process. The entire body of people involved in the decision are the Decision Making Unit or DMU. Your goal is to identify the key person who has the power to say "Yes!" to your proposal. To do that, it helps to understand the various roles people play.