- "That thing in your chest is based on unfinished technology."
"No, it was finished. It has never been particularly effective until I miniaturized it and put it in my—"
"No. Howard said the Arc Reactor was the stepping stone to something greater. He was about to kick off an energy race that was gonna dwarf the arms race. He was on to something big, something so big that it was gonna make the nuclear reactor look like a triple-A battery."
- ―Nick Fury and Tony Stark[src]
The Arc Reactor is a power source designed by Howard Stark and Anton Vanko in an attempt to replicate the Tesseract's energy. There are two main versions of the Arc Reactor: the original, full-scale, industrial version and the miniaturized "chestpiece" version that was perfected by Tony Stark.
In the aftermath of World War II, Howard Stark studied the Tesseract and wished to harness its energy, having developed the idea of providing a limitless power source that could provide clean, renewable energy for the future of mankind. Unable to harness its power, Howard began working alongside Anton Vanko to find an alternative and managed to create the first Arc Reactor, which Howard began to develop through his company, Stark Industries. However, Howard considered the reactor to be simply "a first step" to a much bigger project.
While Howard saw the Arc Reactor as a way to create a new, cleaner method to replace nuclear power, Anton only saw it as an idea he could sell to get rich. Due to this, Howard accused him of espionage and had him deported back to Russia, an event that later motivated his son, Ivan Vanko, to use the Arc Reactor technology to seek revenge on Tony Stark for ruining their lives.
Eventually, a large Arc Reactor for industrial energy production was created to power Stark Industries Headquarters in Los Angeles. Howard developed a theoretical new element which would be the key to completing the perfect Arc Reactor based on the Tesseract. However, he was unable to synthesize it due to being limited by the technology available at the time, and the Arc Reactor project soon hit a standstill. Knowing he wouldn't be able to truly harness the power of the Tesseract or create the perfect Arc Reactor in his lifespan, Howard left a blueprint of his theoretical new element hidden within a model of the 1974 Stark Expo along with a recorded message to his son with clues about the Stark Expo model's true nature hoping he would rediscover it and finish his work. The message along with his original research were left at S.H.I.E.L.D.'s custody so they could one day give them to Tony while the Stark Expo model was left at Stark Industries.
In the years after Howard's death, the Arc Reactor project became a non-priority to the company as it was steered towards mainly producing weapons, with the then acting CEO, Obadiah Stane, dismissing the clean energy project as a "publicity stunt".
During the Ten Rings attack and capture of Tony Stark, a bomb exploded near Stark, causing shrapnel to enter his body near his heart, threatening his life. Dr. Ho Yinsen removed most of the shrapnel but some were too close to his heart so he created a way to stop the shrapnel by using a powerful electromagnet and a car battery. Stark knew that to stand a better chance of survival he had to replace the relatively weak car battery. Thus, he adapted the design of the large Arc Reactor that powered his factory and created a miniaturized reactor that could fit in his hand, giving him a compact and powerful power source that fit directly into his chest and was guaranteed not to fail from normal use. In order to escape from the Ten Rings captivity, Stark and Dr. Yinsen created a rudimentary suit of powered armor to help them escape.
Once Stark got back to America, he suggested that Stark Industries should focus on the Arc Reactor once again, which Obadiah Stane remained skeptical about until he saw the miniature reactor. And his A.I. J.A.R.V.I.S. created a much more powerful version of the miniaturized Arc Reactor, modified to independently power more advanced versions of his armored suit, which he later dubbed the Iron Man suit. Stane continuously pressured Tony to let him patent the miniature Arc Reactor so he could pitch it to investors in order to keep the company afloat, but Tony refused to.
Obadiah Stane commissioned William Ginter Riva and other Stark Industries scientists to duplicate the miniature version of the Arc Reactor to use it in his own suit of powered armor; however, they could not, believing the technology was not yet possible. Stane admonished that Stark was able to do it himself in a cave using even less resources. Ultimately, Stane stole the Arc Reactor from Stark's chest to power his Iron Monger Armor.
During the Duel of Los Angeles, Stark and Pepper Potts destroyed the Iron Monger suit and killed Stane by overloading the Arc Reactor powering the Stark Industries facility, discharging a massive amount of electricity through the suit and electrocuting Stane, who then fell into the exploding reactor.
After the battle against the Iron Monger, Stark built backup Arc Reactor in his suits to so they are able to function without his personal Reactor in his chest.
Soon, Stark eventually learned that the Palladium cores from the Arc Reactor were poisoning him as the Arc Reactor burned through them, which was accelerated by his use of the Iron Man armor.
Tony attempted to fix this completely by finding a possible substitute for Palladium without success. After finding out about this, Nick Fury gave Tony his father's original research regarding the new element which would complete the reactor. With it, and after finding the blueprints within the Stark Expo model, Tony was able to synthesize the element. This created the "perfected" version of the Arc Reactor Howard originally envisioned, and along with saving Tony's life.
At the same time, Ivan Vanko produced a replicated version of the miniaturized Arc Reactor, although the replica was lower in energy output. Vanko's designs were later improved and used in the Hammer Drones he helped create.
Return to Alternative Power
Eventually, Tony Stark decided to continue his father's ideals to use the Arc Reactor to provide clean energy for the world. In order to capitalize on this ideal, Tony Stark created a redesigned Industrial Arc Reactor to power the newly-built Stark Tower in New York City. The tower was completely removed from the city's power grid and ran entirely from the Arc Reactor in order to make Stark Tower a “beacon of clean energy” and show the world the capability of Arc Reactor technology on a large scale. Even though it was only a prototype, the building was capable of maintaining itself for an entire year.
A New Life
Following the battle on the Norco, Tony Stark studied Extremis in order to cure Pepper Potts, and used a variant to survive his shrapnel removing operation. No longer requiring an Arc Reactor in his chest, he later drove to the ruins of his Mansion and threw the Arc Reactor to the ocean.
Following the Avengers' mobilization in order to partake in the War on HYDRA, Tony Stark created Iron Man armors that had built-in arc reactors in them, as he no longer required one in his chest.
Destroyed in Battles
By the end of the Clash of the Avengers, Iron Man and War Machine flew after the escaping Captain America and Winter Soldier. Falcon also flew after the two, so War Machine asked Vision to disable Falcon's suit with his laser beam. Vision, however, missed Falcon and hit War Machine's Arc Reactor, causing him to crash and seriously injuring him.
Later, in the HYDRA Siberian Facility, Iron Man fought against Captain America and Winter Soldier. During the fight, Winter Soldier tried to remove Iron Man's Arc Reactor with his prosthetic arm, only for it to blast out a Unibeam, which disintegrated the arm. Captain America then used his shield to disable Iron Man's suit by destroying the Arc Reactor.
Two months later, a set of Arc Reactors was transported from the Avengers Tower to the New Avengers Facility on a plane. During the transition, Vulture hijacked the plane in order to steal the cargo, but Spider-Man prevented him from doing it, causing the plane to crash. On the ground, Vulture tried to fly with the Arc Reactor container, only to cause the Vulture's Exo-Suit to explode, with the Arc Reactors as well.
In an alternate 2012, Tony Stark helped Scott Lang temporary disable the alternate Stark's Arc Reactor so that they could steal the Tesseract and use the Space Stone inside it in order to resurrect people they had lost. The disabling was only temporary, and the Arc Reactor was fixed shortly after Loki escaped with the Tesseract.