UBCS:Umbrella Bio-hazard Countermeasure Service
The first time you truly meet any UBCS member (if memory serves right) is in Resident Evil 3:Nemesis
The more popular characters are Carlos Oliveria, Nicholai Ginovaef, & Mikhail somethin or other. UBCS is a merc force of Umbrella 'designed' for 'cleaning up their mistakes'
RE:3 Merc's mode allows you to play as either Carlos (medium) Mikhail (easy) or Nicholai (Hard)from the UBCS. I base them as easy or hard depending on what they originally start out with, i.e. Nicholai starts w/ a handgun, a knife, and an herb or two.
The term U.B.C.S stands for Umbrella Biohazard Countermeasure Services from the Resident Evil video games.They're owned by the Umbrella Corporation and are a different unit from the Umbrella Special Forces Unit (HUNK's unit, also known as the Umbrella Security Service) and specializes in rescue operations during biohazard outbreaks. Although they've been very successful in every operation, due to their high mortality rate the unit is comprised almost exclusively of convicted war criminals and mercenaries for hire from around the world that served their national militaries and joined the UBCS as an alternative to capital punishment for any crimes they may have been caught committing. The unit is comprised of almost 120 operatives, divided between four platoons (with two or three squads per platoon).
For example Carlos in the game Resident Evil Nemesis is in the UBCS.