Is it possible for there to be some sort of dream character that we all dream about from time to time? If so, what would he do? Would he enhance lucidity? Teach us new dream skills? Or would he attack us? 
Could multiple people have a shared dream, and encounter him/her all at once?
Well, according to Carl Jung it’s possible. He calls these entities “archetypes”. They apparently have their origin in the immense reservoir of the collective unconsciousness of mankind.
So it’s quite possible that they can be found in the dreamworld of every civilization on Earth. Ofcourse these archetypes are coloured by your culture and they can appear in your dreams in many forms, but their meaning stays the same. I don’t know if you could use them for LDing though.
The main archetypes are: Shadow, Anima/Animus (male/female soul), Syzygy (the divine couple), Child and Self.
I hope this answers your question a bit 
Well, archetypes have the same meaning from person to person, but their form varies enormously. But I think what we’re looking for here is a character that takes the same form for everyone. I can’t think of any right now, but… I don’t know. Maybe something from stories, like santa or the tooth fairy. Or some other fantasy character that we all know about.
sure why not it DC are a creation of our mind… as we know it. then if i have a SD with you then some of my DC come along for the ride you could met it… does that make sense?
Hm perhaps angelic entities then? Most people see them in a NDE, but they can also enter high level LDs. And their shape seems to be pretty specific.