He has been a warm and welcoming presence in the community. The responsibility of the host is to serve the community by facilitating discussions, answering questions, and greeting newcomers.
Hosts can also enhance the interaction by asking questions of the various participants.
These answers would add to the community's content. To that end, I also think that a host, while more visible, should be as unobtrusive as possible. The exception would be that rare person who, by name recognition, or by force of magnetic personality, can bring about the emergence of a community around themselves. I think I pretty much am myself. I hide some of my personality warts, but when people interact with me, they get me.