I have read most of the accounts on this shadow with red eyes and I believe that I have been followed my whole life by something similar.
When I was a child, I used to be found talking to the ceiling in my bedroom and my parents said I described my "friend" as black with red eyes. They told me about this when I finally approached them about the shadow with red eyes I've been seeing in my room (which was the same room I was in when I was little).
I continued to see this figure until I moved out of my dad's house and I started seeing it in my new house, except it had yellow eyes this time. Later I joined the military and continued to see it even when I went to combat (it's eyes had turned red again at this point). And to this day it has appeared several times in my current house. Even my wife has seen it.
Now the one major difference I have found in everyone's story and mine is that the shadow I have been seeing has never tried to hurt me or scare me or anything else. As a matter of fact, it's quite the opposite.
My dad's house has ghosts in it and two of them have been removed by this shadow. One was a guy who always chased me down the hallway to my room every night I went to my room. At about 15-years-old, I finally told the ghost to leave me alone and I saw the shadow appear in my room walk through my closed door and I have not seen the ghost again.
The other ghost he has removed was a little girl who used to sing into our fan at night and wake you up so you can play with her. After I got divorced, I was living with my dad and had my daughter with me. I put her to bed one night shortly after we first got there and I later went to check on her and she was sitting up crying, hiding her face with her blankets rolled up to her feet. She said that she saw a girl who looked very mad roll her blankets up at her and start trying to hit her. A couple of nights later I woke up to my bed shaking and saw the girl standing at the corner of my bed. I yelled at her to leave my daughter alone and threatened her. Just after I got done, I saw the shadow walk into my room and grab the little girl by the arm and drag her out of the room. I have not seen her since either.
When I was in combat I would wake up at night and see the shadow figure sitting in front of my door as if he was waiting for someone to open it, kind of like he was on guard duty.
So when I read all the posts, I thought I would share my experience with this shadow figure since he has seemed more like a guardian for me than a threat.
I have no idea what this means, but maybe it helps someone make sense of their sightings.