Manager Zack is the executive representative you contact when you select an Eco Executive Mansion. He is the representative of the Eco Population on any player-build island, at least after you have attained Eco Executives on the island. He appeared in Mission One: Finding the Truth as the man who owns the Eco settlement when you are choosing which island to settle. If you choose the Tycoon settlement, he claims he will notify Yana Rodriguez. After that, you could take on a quest to trade with him to earn some credits in your mission.
Manager Zack is the Ecos' counterpart of Manager Russel from the Tycoons.
You can obtain his portrait by attaining the "Master Diplomat" achievement, which requires reaching the highest career level for each faction.