Lord Garmadon: Nuckal, if you please.
Sharingan is a special eye that can cause illusions, copy forms of Spinjitsu being used against the user and makes lighting more powerful. Originally from Naruto.
Nuckal hides his Sharingan behind a metal patch and uses it to do Lord Garmadon's dirty work. Nuckal eventually betrayed Lord Garmadon once his Sharingan got more powerful, and he went to go and get the Four Golden Weapons for himself so he could sell them and buy a fez.
Kai stole the Sharingan from Nuckal after destroying him. Before Nuckal had been destroyed he killed Jay and Cole so in anger Kai went out of control and wanted to destroy Ninjago.
??? killed everone in Ninjago so he could steal Kai's Sharingan. After that he brought then all back to life.