His role is bound to the minecrawler-nest objective: you recruit him to help open and defend the collapsed tunnel against the crawlers and their queen, part of the Brotherhood's nest questline.
Old Mine, near the collapsed tunnel: A Brotherhood templar leading the effort against the minecrawlers.
Gor Na Bar can be found in the Old Mine (Templar).
Gor Na Bar: Sleeper guide you.
You: What can you tell me about the crawlers?
Gor Na Bar: What I can tell you about them? Stay away from them, unless you know what you're doing.
You: I need your help. We're going to open the collapsed tunnel, but we need help defending it when the crawlers come out.
You: Can I count on you?
You: And their queen, yes.
Gor Na Bar: What about the ichor? Please tell me you found some other source, I-