Spoilers: (Highlight to reveal)
With Smoke as his template, Noob Saibot planned to return to the netherealm and use Smoke's nanotechnology to create an army of Cyborg-Demons. He was unaware that they were being followed by someone Noob had not seen since before he became a wraith. Smoke instantly recognized their visitor, he was an echo of their past. He was Sub-Zero, Noob Saibot's Brother.
Noob Saibot was surprised to see how much stronger his brother had become. If he were still Lin Kuei, still human, he would probably have shown some degree of pride. But as Raiden had revealed during the ordeal with Shinnok's amulet, his soul had become tainted when he died at the hands of Scorpion.
Noob Saibot, the original Sub-Zero, had descended into the netherealm free of compassion. He ordered Smoke to assist him in slaying his brother, his first act as ruler of the Netherealm.
So there you have it folks; Noob Saibot is the wraith form of the original Sub-Zero. I was so shocked when I found this out. I know most of you will consider this shit stiring, but unlock Noob-Smoke, and beat the game with them. You'll find the exact same ending awaiting you.