Reactron was a human supervillain, an enemy of Kryptonians everywhere. Although he has no powers of his own, he has a battlesuit which contains many offensive and defensive technologies including gold kryptonite, many of them especially effective against Kryptonians.
Reactron was most recently with the United States military Project 7734. He was responsible for the murder of Zor-El in broad daylight in the middle of Metropolis. Recently, he was also used as a bomb in the destruction of the planet New Krypton. (Comic book storylines: Superman: New Krypton, The Last Stand of New Krypton).