This is a list of important NPCs that the player characters would likely see on a fairly regular basis.
Marlene Magicwrench The overall leader of Oasis, and the one in charge of most of it's administrative tasks. She mostly focuses on the maintenance of the farm irrigation systems and on keeping the armory well stocked. Not much of a social person, she leaves her workshop only when she has to, and delegates many tasks to her helpers.
Quartermaster Roger Burns A former NCR quartermaster, Burns is in charge of the Oasis's logistical concerns. Figuring out how much food they can spare, making sure they have weapon and ammunition supplies for the guards, and also negotiating trade for the various things that the Oasis can't produce all fall on his shoulders.
Captain Williams A massive and fearsome looking Super Mutant, Williams acts as the leader of the Oasis guards. Any disputes about the rules are arbitrated by him, and he also keeps track of who has been banned from the settlement and why. Standing nearly ten feet tall, with a Super Shotgun on his hip and a Super Sledge on his back, Williams isn't someone to mess with, but the FEV didn't rob him of his quiet, direct intelligence or his ability to see the different sides of an argument. All tasks related to defending the Oasis and keeping it's guard force working smoothly are his.