Reactron

"You Kryptonian kids really aren't too bright, are ya?"

- Reactron to Supergirl

Benjamin Krullen, better known as Reactron, is a supervillain who first appeared in Doom Patrol Vol 2 #10. Despite first appearing as a Doom Patrol villain, he is primarily known as the archenemy of Supergirl.

History
Discontent with the way he his life was going, Benjamin Krullen decided to join the U.S. Army. One night, during guard duty at a top secret government project, he was seriously injured. In order to keep Krullen alive, the scientist in charge of the project gave him a special suit, the StarSuit. Upon obtaining the suit and newfound powers, Krullen abandoned the military and later resurfaces as a supervillain; taking the name Reactron.

He later faces the Doom Patrol and Power Girl and is seemingly destroyed after overloading on Negative Woman's energy; but it is revealed he survived and became a member of the Suicide Squad. He is presumed to be killed again when Deadshot shoots holes in his containment suit, causing him to go critical; but he survives this as well.

Some time after, Reactron became a member of the Nuclear Legion alongside Professor Radium, Geiger, Mister Nitro and Neutron. The Nuclear Legion was hired by the Secret Society of Super Villains to invade Blüdhaven and assist the Nuclear Family in recovering the source of a radiation leak. While there, the group fought the new Atomic Knights.

Reactron later went on to become a thorn in the side of Supergirl. He fought against her on more than one occasion, but Supergirl was never able to stop him for good. A short while later, Reactron was recruited by General Sam Lane as part of a special contingent to deal with threats of an extraterrestrial nature. He was outfitted with a piece of Gold Kryptonite and partnered with renowned Superman villain Metallo. The two began wreaking havoc in the streets of Metropolis with the sole intent of drawing out random Kryptonians who had recently arrived on the planet Earth. Upon doing so, they followed the Kryptonians back to their home in the Arctic, New Krypton, and began laying siege to the city. During the battle, Reactron killed Supergirl's father, Zor-El.

After murdering her father, Supergirl went on a manhunt for Reactron to have him stand on trial at New Krypton for his crimes. After eventually finding him, the Girl of Steel managed to defeat and capture Reactron with the help of Thara and Chris. However, during his imprisonment, Lex Luthor sends a robot double of himself with Brainiac on a mission to attack New Krypton. While there, the Luthor robot tampers with the body chemistry of the previously-captured Reactron. Shortly thereafter, Reactron kills himself, initiating a chain reaction which ultimately destroys New Krypton and all but a handful of its 100,000 inhabitants. Supergirl's mother Alura In-Ze (who had assumed leadership of the planet) is among the casualties.

During the Blackest Night storyline, Scarecrow drugs Supergirl with his fear toxin, which causes her to believe she is fighting Reactron; reanimated as a Black Lantern.

Powers and Abilities
Reactron has the ability to generate radiation from his body. He can focus this into concusive blasts. Currently, Reactron is also equipped with a heart made of a Gold Kryptonite variant, which allows him to render a Kryptonian powerless for 15 seconds.