Engineer

The Engineers hideout is the large church in Lugowniki. He takes part in the Main Quest line. Just as the Biologist he will give minor daily quests. But his quests consist of collecting certain items. The Engineer lost his family after the incident and his daughter will haunt the volunteer in specific areas.

You are required to meet the engineer upon reaching a point in the quest that requires you to get a mob scarer. This enables you to obtain the UV Light which is toggled by holding "T". (Hint, the UV is a quintessentiak component, and you will need it for various story missions). After completing this mission you are able to complete retrieval quests which give you exp and loot. With each level of trust, he grants you better rewards.

He also sends you on a quest to retrieve something from raiders.