Deleter?

The Deleter was probably pvt. James (the one with the mustache).

When Samus arrives at the Exam Center, she finds James already there. When Maurice tries to access the data on the computer, all files from the mainframe appear to have been deleted. Coincidence? He was probably there to quickly erase the data in the first place.

Later, Samus follows a suspicious looking Marine who she suspects is the Deleter. She ends up finding the blond researcher who claims to be Madeline Bergman. The Deleter watches them talk from above (we see his point of view). When Samus leaves, he walks towards Madeline, probably with the intent to kill and silence her. We see him approach her from his point of view; she looks at him fairly unsurprised, the screen cuts to black and we hear a shot, naturally assuming that he killed her.
However, later in the game, we learn that Melinda is, in fact, Melissa Bergman, or MB, and far from helpless. When Samus later returns to that room, she finds pvt. James lying dead on the floor, suggesting that he unsuccesfully tried to kill her, and therefore most likely was the Deleter.

Ridley was the fuzzy white little creature that Samus encountered in the jungle sector. She later sees it eating from dead animals. It eventually mutates into the lizard-like beast that attacks her outside the Exam Center (Samus finds the little creature's shed-off skin). It later mutates again, shedding off the lizard skin (which Samus sees hanging at a wall over a door) and emerging as the fully grown Ridley.


Fate, it seems, is not without a sense of irony - Morpheus