Gregory is a resistance general and is responsible for a lot of what the resistance does. He is a Vietnam war vet that served alongside Bill. They met up again when Bill moved to the Texas base. Not much is known about how Gregory got into the resistance and managed to supply the resistance with military grade tech and an underground base.
Gregory is old, bald, and has a nice mustache. He looks very good for his age, and manages to keep himself healthy enough to keep leading. He just wears a normal military outfit, and sometimes a beret.
Gregory is very calm and charismatic. He tries to be as helpful as he can when he's not working. This is seen when he was handing out scantily clad bikinis to women when they discovered a hot-spring. He sometimes loses his composure when giving a speech or trying to motivate his men, but most of the time remains composed tries to figure what the best decision is to take. He is very loyal also, it's something that means a lot to him. And he despises traitors more than anything else. This can be seen when he stays loyal to Aki, and is killed by Arthas.