https://www.pcgamer.com/noob-saibots-mortal-kombat-11-trailer-will-make-you-jump-out-of-your-skin/

The Mortal Kombat 11 lineup has grown again, this time with the addition of Noob Saibot, a shadowy ninja who used to be Sub-Zero before Scorpion killed him in the original Mortal Kombat tournament as payback for killing Scorpion. 

The Mortal Kombat lore hole is a deep one, but the crash-course is that Sub-Zero offed Scorpion so Scorpion, after being resurrected by Quan Chi, offed Sub-Zero. Then Quan Chi resurrected Sub-Zero too, because I guess that's how he gets his kicks, but by that time his younger brother had become Sub-Zero so OG Sub-Zero called himself Noob Saibot instead, which is actually the last names of Mortal Kombat co-creators Ed Boon and John Tobias spelled backwards. Got it?