(Thunderbolts I#61 (fb) - BTS) - The Iron Cross armor was created in the 1940s and worn in service of Germany by several different people over the years.
(Thunderbolts I#62 (fb) - BTS) - Zemo was born as the son of infamous World War II scientist Heinrich Zemo.
(Thunderbolts I#62 (fb) - BTS) - After Earth's heroes left Counter-Earth Franklin, the planet suffered a series of natural disasters that led to global catastrophes. The problems didn't end even after Doctor Doom shifted the world from its pocket dimension to Earth-616's solar system. Throughout the ongoing crises, Germany remained one of the few nations that managed to maintain a thriving economy. As a result, the European country quickly rose to power and prominence.
(Thunderbolts I#62 (fb) - BTS) - Hoping to capitalize on Germany's newfound importance, the World Party took center stage, now claiming to be a political alliance with tentative ties to, among others, France and the United States. Baron Heinrich Zemo was tasked to head up an elite team of super powered operatives.
(Thunderbolts I#60 (fb) - BTS) - Helmut Zemo was the latest person to operate the Iron Cross armor.
(Thunderbolts I#60 (fb) - BTS) - Heinrich Zemo made his son second in command of the Thunderbolts, a group of international heroes operating out of Germany, but fighting for all of Earth. The Zemos secured the services of France's heroine Chain Lightning and the American mercenaries Makeshift, Solarr and Phantom Eagle.
(Thunderbolts I#62 (fb) - BTS) - The Thunderbolts operated together for at least eight months. Zemo assured their allegiance by offering them a comfortable, luxury filled lifestyle.
(Thunderbolts I#61 (fb) - BTS) - Ever suspicious, Zemo had listening devices planted on all the members of his team, even his own son, so he could always be aware of what they were up to.
(Thunderbolts I#62 (fb) - BTS) - Iron Cross and the other Thunderbolts agreed to help Baron Zemo spearheaded a World Party approved plan to give Germany world dominance. The country would be launching a satellite that they claimed would help restore global communications. In reality, it was designed to only allow Germany access, which would give the country control over the world economy.
(Thunderbolts I#61 (fb) - BTS) - Iron Cross used his engineering background to aid in the construction of the rocket.
(Thunderbolts I#60 (fb) - BTS) - Zemo took the Thunderbols to the former Soviet Union to locate and secure a prototype fuel injector assembly for the rocket.
(Thunderbolts I#59) - While in Russia, Zemo's team came across the unconscious bodies of the Thunderbolts who had just been transported to Counter-Earth following their fight against Graviton.
(Thunderbolts I#60) - Zemo immediately assumed the worst, suspecting these unknown mercenaries were sent to thwart his mission. The Fixer tried to buy time for his teammates to recover, using the weapons in his Tech-Pac to keep the Thunderbolts at bay. Moonstone managed to sow momentary dissension in their ranks by suggesting the World Party did not trust the Thunderbolts enough. This infuriated the fiercely loyal Iron Cross who immediately flew off the handle, but his father saw through her ruse. He slapped his son and told him to stay silent. However, Zemo the elder did buy Moonstone's next lie, believing they were merely mercenaries hired to check if they were doing their duty. He allowed them to leave.
(Thunderbolts I#60 - BTS) - Zemo's Thunderbolts retrieved the fuel injector and returned to Germany. When Earth's Thunderbolts learned of Germany's upcoming launch, they decided to hijack the rocket and use it to leave Counter-Earth.
(Thunderbolts I#61) - Zemo's
Thunderbolts continued to work on the rocket after returning from the
Soviet Union. Iron Cross was furious when he overheard Solarr and
Makeshift openly discussing the true nature of the rocket's payload.
Ever ambitious, he set them straight but Makeshift correctly pointed out
that the ever ambitious Iron Cross and he smirked when the ever
ambitious Iron Cross forcefully set them straight.(Thunderbolts I#62 (fb) - BTS) - Earth's Thunderbolts made it from Russia to Germany hours before the rocket launch. Fixer created fake IDs for all of them so they could go on a fact finding mission inside the base.
(Thunderbolts I#62) - Iron Cross was working on the launch tower with Abe Jenkins (MACH-3), who began to doubt it could be centenarian Helmut Gruller inside the armor. Jenkins was impressed with Zemo's dedication to his engineering craft. For a would-be world conqueror, he sounded young and hopeful.
(Thunderbolts I#62 - BTS) - 46 minutes before the launch, the Fixer abandoned his allies to carry out a mission for Earth-616's Helmut Zemo whose digitized essence was stored inside his Tech-Pac. Zemo threatened to shut down the Tech-Pac's life-preserving systems if Ebersol didn't find him a new body.
(Thunderbolts I#62) - After entering the facility, Fixer used gas to cause a distraction, swiftly knocking out Zemo and Solarr and then disabling Makeshift, Chain Lightning and Phantom Eagle. Iron Cross was the only one left standing, his armor protecting him from Fixer's attacks. He attacked his opponent from behind, but that only gave Fixer the opening he needed to instruct his Tech-Pac to make a connection with the man inside the armor. He started to transfer Zemo's essence from his Tech-Pac to his new host.
(Thunderbolts I#62 - BTS) - Once the transfer was complete, Zemo quickly made his new body his own (see comments). As his first act, he used the Iron Cross' weapons to gun down and kill his unsuspecting father.
(Thunderbolts I#62 - BTS) - The rocket launch went ahead as scheduled, but Earth's heroes made sure it exploded before it could deliver its payload. MACH-3 and Fixer then put out a worldwide broadcast, revealing Zemo and Germany's deception. The surviving members of Zemo's Thunderbolts were presumably incarcerated (see comments).