Stalker is an antagonist of the superhero comic known as Extinctioners, he is one of several humans known as the Hunters who were sent to Alden in the past to ready the planet for the arrival of humans and recolonization at the word of Noah Adam Mahn, however due to an accident they lost contact with the rest of humanity and as a result began to utilize tactics that could be considered war-crimes by today's standards (though it still unknown whether or not Mahn's tactics are criminal or accepted by the other humans, who have yet to arrive on Alden).
As for Stalker himself, his real name is Ethan Stalworth and he wasn't hired to be part of the team for any type of scientific background. Pure and simply he is a hunter. His is a trained field tracker and killer and he enjoys his job, a lot.
While many high tech weapons are at his finger tips, he prefers using low-tech hunting tools to capture his prey. Particularly knives and long range rifles. Many of his fellow Hunters believe he is crazy, a reputations well earned, and it's no wonder he was partnered up with the humanimal Tracker, Lynx Wylde, because both have personalities that compliment one another.
Powers and Abilities
Stalker's original character sheet.
Stalker has not shown superhuman abilities, however as a Human he has access to technology far beyond that of Alden - yet prefers to utilize more primitive (yet still lethal) weaponry such as rifles, knives and similar - like Lynx he is also a savage killer and a shameless sociopath, seeing torture and death as forms of entertainment.