The Extremists are a group of characters based on Marvel villains. They come from Earth 8 also know as Angor. The Champions of Angor are called The Assemblers (one of my favorite parody names). Morrison showed an updated version of DC's Marvel U during his Multiversity.
The Extremists consist of:
Lord Havok the Dr. Doom of Earth 8
Gorgon who is a parody of Doctor Octopus
Dreamslayer a parody of Dormamu
Tracer is a parody of Sabertooth
Dr. Diehard is a parody of Magneto
Lord Havok from Multiversity:
Marvel has done some cool things with their DC doppelgängers over the years. I'm glad DC is bringing back Angor and The Extremists. We aren't going to be getting any crossovers any time soon so we may as well enjoy this.