Sentinels are giant robots which are programmed to destroy super-powered beings. They were created on a previous Earth to rid the world of these beings. Sentinels are controlled by a supreme intelligence named 'Master Mold'. They can shoot energy out of their hands.
Some 20 years after they were created, Master Mold decided to turn the Sentinels against the humans. The Sentinels eradicated most humans and mutants from Earth. Later, an event occurred which sent some of the Sentinels flying into space and they lost touch with Master Mold. Before landing on Bara Magna, Kakamu encountered five Sentinels and allied with them. Kakamu told them his enemies, and downloaded his knowledge into them. The remaining Sentinels on Earth were destroyed when Blackout used unstable hadrium to destroy the planet.
Because the few Sentinels remaining knew about Blackout, they tracked him down and fired energy at him. Blackout responded by taking them off-line and having them taken to the lab to be studied and reverse-engineered. They were later tossed into the Theta Gate, somehow causing dozens of Sentinels to emerge.
- They were Monarch's worst enemies.