The Peacekeeper is a war machine developed by Dr. Tenma and presumably Dr. Elefun in the 2009 adaptation of Astro Boy. It is built to run off core energy, be it red of blue, and possesses adaptative technology, granting it the ability to absorb other machines, weapons, people and even buildings.
In the initial weapon test before its unveiling to the public, the Peacekeeper was intended to run on positive blue core energy, but the warmongering President Stone sabotaged the test, ensuring that the robot instead ran on red core energy, which was negative, unpredictable and highly unstable. After obliterating all target drones, it turned on its human masters. A security screen was brought down to protect the President and science team, and the Peacekeeper was eventually shut down, but not before its attempts to break through resulted in it vapourising Toby Tenma.
The robot was later reactivated when Astro escaped the President's clutches, still carrying the blue core. After the red core was loaded into the Peacekeeper, it assimilated President Stone, who took control of the robot's and began absorbing more technology into itself, including the Spirit of Freedom battleship, growing to monstrous heights and attacking the city in search of Astro. The little robot fought valiantly, but ultimately realised the only way to save Metro City was to merge the red and blue cores together, sacrificing himself but ultimately destroying the Peacekeeper, leaving a slightly bruised, defeated and confused President Stone to be dealt with by the police.