Nightkin

The Nightkin were an elite warrior caste in the Master's super mutant army. They can be found in the upper levels Cathedral, as well as inside the Mariposa Military Base and the nearby cells surrounding it in the form of random patrol encounters. They were superior to other supermutants in skill, equipment and weaponry.

The Nightkin were all equipped with cloaking devices, the Stealth Boys. The only gaming effect of this is to give them a slight ethereal look, as it does not affect the PC's chance of hitting them.

The Nightkin in Fallout Games
The Nightkin appeared in the first Fallout game in the Cathedral and Mariposa Military Base. They also appear in Fallout: Brotherhood of Steel. The Nightkin also appeared in Fallout 2 as a hostile encounter on the World map. The mutant commando advanced character class in the cancelled Fallout d20 was based on the Nightkin.