sadly enough this is more possible than most gman theories
Gman is a dead monkey combined with charlie sheen and chuck norris and is the red eyed man from the book wrinkle in time
and at the end of half life 1 the portal gordon freeman took lead to his room where he grabbed his stuffed...
you know what i am sick of these theories lets just say gman is charlie sheen combined with chuck norris and leave it at that till the canonical answer is made