Noob Saibot is the alter ego of Bi-Han after his resurrection as a wraith.
Bi-Han was the original Sub-Zero in the first Mortal Kombat game. After Scorpion killed him, Bi-Han was resurrected and transformed into the shadowy wraith known as Noob Saibot. His new identity reflects a darker version of the warrior he had been before his death.
The name Noob Saibot is a reversed spelling of “Boon” and “Tobias,” the surnames of series creators Ed Boon and John Tobias. The character first appeared as a hidden opponent in Mortal Kombat II, although his backstory and identity were developed more fully in later games.
The younger Sub-Zero, Kuai Liang, is a different person and later inherits the Sub-Zero mantle. That distinction often causes confusion: Bi-Han is the original Sub-Zero, while Kuai Liang is the better-known successor in many storylines.