The Boss, also known as The Joy, The Mother of Special Forces, Mercury Lady and Voyevoda (Russian for "Warlord"), was the "final child of the Philosophers," and the mentor of Naked Snake. She was the founding leader of the Cobra Unit, in which she was known as "The Joy," however, when they were disbanded at the end of World War II, she was granted the codename of "The Boss." Together with Naked Snake, she developed the technique of CQC.

In the Virtuous Mission, The Boss wore a bandana and Olive Drab uniform (which appeared to be the staple FOX unit battle fatigues). After Naked Snake pulled the bandana from her head when she threw him from the bridge in Dolinovodno, Snake wore it during Operation Snake Eater and later wore it in tribute to her. The Boss commented on his inability to let go of the past by taunting him for wearing her bandana as a reminder of her during his mission.