Ah come on now... hope it's Beel! "Where is Beel?" his constant "Suckeeh is maaahn (mine)" are giving me headaches tbh.
If they're focusing on the more human side, it's not going to be Bill. Or Eric. Tumblr speculation is on either Jason or Laffy (who's a supe, but still human).
It could be Arlene, she's from the beginning and she's still human. Terry? But then you start really stretching the definition of 'major'.