TeamTNT is a well known, prolific group of mappers, most known for creating TNT: Evilution episode of Final Doom, as well as several free level packs for Doom II, including Icarus, Eternal Doom, and Daedalus. Most of TeamTNT has split up, but several members are still around. Try Halderman maintains the /idgames archives, Cadman leads the "Community Chest Part Deux" project, among others. They have also created the Boom source port.
There are no registered leaders of this group. This can be granted to the right person on request. Also why don't you join the community, we welcome creators and consumers alike and look forward to your comments.