AGAIN with the IT IS/IT IS NOT a prequel.
Tecnically speaking it's not, no characters from ALIEN is here (the dead SJ is NOT in PROMETHEUS, nor the Derelict, we get members of the same race and a same class ship) and the event will not lead to the Nostromo nor the Derelict crash.
Now save from the people who know ALIEN and who are fans, the average audience do not see the hint to ALIEN.
The way the tittle appears, the music etc....
WE do! It's a gift to the fans who will spread the word that the movie is actually related to ALIEN.
Scott don't want to redo ALIEN neither use the original xenos.
The trailer is very ALIEN like storywise, a ship land on an alien planet, they explore, stumble on some shit, monsters are on the loose... It's just a trick to make us fan root for it (and usually it's to serve the same stuff again and again as hollywood usually do) we will feel in familiar ground then he will rip the rug from under our feets and take us somewhere else..
Also from a marketing point of view they dont want to call it ALIEN because the franchise is dead in the water and also Alien = AVP in the mind of the average movie goer and the new generation that Fox wants to bring in the theatres.
I think this is an engineer/jockey in its original form.
What is that ? A follower/Mechanic ? He looks to have a "beard" or what's left of it.
Maybe it's the first stage of a transformation.
But f**ked from a fight or burn with the humans but he is portraited in the movie much larger.
but he's seems to wear the same uniform as the crew use to wear.
He's a crew member that get infected, mutated.
You can see him jumping on the flamethrower dude with his suit on.
My take is that he's either one of the many f**ks up that the ampules/vials causes or tranforming himself into an Engineer.