Joe

From DoomWiki.org

The name Joe, in the id Tech 4 SDK, is the default name for any NPC in Doom 3. The name "Joe" can only be seen with the noclip console command. These Joes have no dialogue. An exception is that one of the soldiers in Mars City is named "Ronn", but you can only get to Ronn with the noclip command as well. It is not known if the name refers to any real person. An NPC in Mars City Underground, thought to be a Joe, is actually T. Brooks. Another supposed Joe is actually just a static object you can pass through.