He was eventually forced to retire with a purple heart when he was shot in the shoulder, rending his left arm useless. He was recruited into the NCR when they first moved into the Mojave, where he was known for being an expert hunter from Goodsprings.

He is known to the Legion as Niveus Nex, or White Death. Marksman Mark is a retired NCR veteran, one of the finest shots in all of the First Recon. Upon approaching him, he tells you to to screw off, but with a bit of prodding, he will tell you his problem. He's sitting at one of the tables, with several whiskey bottles in front of him, drunker than hell. In the Tops, in the Four Aces Theater, there is an old man, named Marskman Mark. I think there should be an incentive to kill all four of them, other than the obvious Mercy which you get for killing the Deathclaw. In Fallout:New Vegas, there are four Legendary Creatures. Hey If you were interested in doing more on this mod or a similar mod idea I have a mod from my quest idea thread that you'll enjoy

Fallout new vegas legendary creatures