Sven, Eric, and Harlan Kleinstock are identical triplets with the power to merge into each other. Finding salvation in Magneto's words as members of his Acolytes, the Kleinstock Brothers were very radical and had no problems committing murder on those deemed as "flatscans." During their first confrontation with the X-Men, their brother, Eric, was shot and killed by Tom Corsi. Harlan and Sven couldn't have cared less, as they considered Eric the "black sheep" of the triplets. Once they discovered the one they were searching for was a child with down's syndrome, the Kleinstocks, along with their teammates Joanna Cargill and Unuscione, fled the scene.
The twins stayed with the Acolytes for several missions, and survived the fall of Avalon by banding together with the X-Man Cyclops. Crash landing in the Australian Outback, the Kleinstocks didn't appreciate Cyclops' leadership, but stayed near despite their dislike for him. They were eventually turned into the authorities after they found the X-Men's former base of operations.
During the attack on Mt. Wundagore, the Kleinstocks stuck by with Fabian Cortez and battled the Knights of Wundagore with ease. Later, the Kleinstocks joined the faction of Acolytes who were sent to attack the X-Mansion. After searching solace for their actions, those Acolytes were turned away by Charles Xavier and abandoned by their former teammates. The Kleinstocks then attacked Genosha alongside the renegade Acolytes, but were taken down by Cargill and her mercenaries. It is unknown if the Kleinstocks survived the attack on Genosha, or if they retain their powers after M-Day.