Krang (Out of the Shadows)

Krang is the true main antagonist of Teenage Mutant Ninja Turtles: Out Of The Shadows. He is an alien warlord from another dimension seeking to conquer ours. He had sent three components of a machine to our dimension that, when united, would open up a portal to his dimension.

History
When Shredder got hijacked while attempting to escape by teleporting, he was transported to another dimension where he met Krang. krang provided him with a mutagenic compound in exchange for his promise to find three components of a machine Krang sent to Earth in ages past that open a portal to his dimension when united.

After Shredder completes the portal device, Krang emerges with his war machine, the Technodrome. Krang then betrays Shredder, freezing him and locking him away with his collection of other defeated foes.

The Turtles then confront Krang aboard the still-assembling Technodrome. They locate the beacon around which the Technodrome is assembling and hurl it back through the portal, taking Krang and the rest of the Technodrome with it while April, Casey, and Vern then shut the portal down. As he disappears, Krang swears he will return for revenge.