Glenn was a dog in Los Angeles.
Not much is known about the dog as he is only seen once when trying to run to a marine named Jason Lockett. He looked at Glenn's collar and it had the name Glenn on it. A marine was then heard saying "Who's the idiot naming dogs these days?". As they were talking about Glenn, the marines were ambushed by alien infantry. It is unknown if Glenn was killed or simply ran off. Since nothing is heard about him after the ambush we can only guess what happened to him.