The Arc Reactor was a fusion type power source featuring a palladium core, and was the initial power source of the first Iron Man suits, and was later modified to an advanced level by Tony Stark to power his more advanced suits, as it kept on improving. During the events of Iron Man 2, Tony re-discovered and synthesized a new element theorized by Howard Stark, as a clean and safe core alternative to palladium core. This not only stopped palladium poisoning of Tony's body but also reversed its effects, saving his life.
The Stark Industries HQ in Los Angeles was once powered by an Arc Reactor, but it was destroyed when Pepper Potts overloaded it and Obadiah Stane with his Iron Monger Armor fell into the reactor. It is unknown what happened to the reactor after this event.
Large Arc Reactor
Palladium Arc Reactor Mark I
The Original Miniaturized Arc Reactor was created by Tony Stark and Ho Yinsen while being held captive by the Ten Rings in Afghanistan. Captured to build the Jericho missile, Stark, with the help of Yinsen, instead used the Ten Rings' spare parts and old Stark-Tech missiles to create a miniaturized palladium-cored Arc reactor to power Tony's electromagnet that keeps the shrapnel of one of Stark's own missiles from reaching his heart. Capable of generating 3 GJ/s, it can keep Stark's heart running for 50 lifetimes, as mentioned by Yinsen. To which Stark responded to that with "Yeah, or something big for 15 minutes". The reactor was later replaced by the Mark II model when Tony returned to the US with the help of Pepper Potts. Tony was forced to don the reactor again after his Mark II model was stolen.
Following Tony's death, the original arc reactor was floated in a lake with the inscription "Proof That Tony Stark Has A Heart" around it as a form of memorial.
Palladium Arc Reactor Mark II
Created by Tony Stark after returning home, the Palladium Arc Reactor Mark II is used to power his electromagnet and his Mark II and Mark III suits. After finding the Mark I suit and rebuilding it into the Iron Monger, Obadiah Stane steals this reactor out of Tony's chest to power Monger armor as he is unable to replicate the technology. Tony faces him using the Mark III powered by the original reactor, but it is inadequate to power his suit properly. Finally, Tony has Pepper Potts overload the Large Arc Reactor powering Stark Industries HQ, resulting in overload inside of Stane's suit, which electrocutes him and knocks him out. Stane, with his suit, fell into the reactor resulting in an explosion destroying the suit, the reactor, and killing Stane.
Palladium Arc Reactor Mark III
The Palladium Arc Reactor Mark III was the reactor used by Tony for six months (the time jump from Iron Man 1 to Iron Man 2) to power his armors and electromagnet in the movie Iron Man 2. It was created to replace the one which was stolen by Stane and later destroyed. It is eventually replaced by an improved reactor as the palladium was slowly poisoning Tony to death. Mark II was a testbed for an Integrated reactor, allowing James Rhodes to steal the Mark II suit.
The New Element Arc Reactor Mark I
The new element Arc Reactor Mark I was the Arc Reactor created by Tony after he rediscovered the element originally discovered by Howard Stark and synthesized it, resulting in the new and more powerful clean energy source. Mark VI was the first suit to be designed with the new model reactor in mind. Sometime later, an enlarged version of the reactor was installed into newly built Stark Tower, capable of providing self-sustaining power for a whole year, as well as an integrated reactor, powering the Mark VII armor.
The New Element Arc Reactor Mark II
Tony eventually replaced the Mark I reactor with the Mark II to power his Iron Legion and electro-magnet. The ones powering the Iron Legion were destroyed when Tony had J.A.R.V.I.S. self-destruct the suits and after having the shrapnel removed from his chest, Tony pitches the one powering the electromagnet into the sea.
The New Element Arc Reactor Mark III
Some time after the Iron Legion's destruction, Tony perfected the Mark XLII's design resulting in the Mark XLIII and its Modular extension, Mark XLIV. Powered by multiple New Element Reactors, the Mark XLIV managed to take down the Hulk during his rampage in South Africa. The Mark XLV also utilized this new generation reactor in conjunction with a new repulsor design to give it better power distribution, resulting in faster and more stable flight, quicker charge times of repulsor blasts in flight (higher charging tone, when power levels inside the suit is high) and instant charge when on ground as well as higher intensity of said blasts (capable of destroying Ultron Sentries in one blast).
The New Element Arc Reactor Mark IV
Utilized by the Mark XLVI and XLVII, this new reactor borrowed ideas from the Mark XLIV's Multiple RT design, allowing for an around-100kg suit to operate even with the main RT damaged or destroyed, and providing greater power distribution which results in equally fast weapons grade repulsor blasts, both while in flight and on ground (despite being fast charging, it does not support instant-blast capability). The main RT's blast (Unibeam) was powerful enough to vaporize the Winter Soldier's Bionic Arm.
The New Element Arc Reactor Mark V
This is the second most advanced reactor designed by Tony Stark. This heart shaped reactor is capable of not only working as power source of newest generation of Iron Man armors, but also being capable of storing the nano-particles necessary in the forming of not only the Mark L armor, but all the modules needed depending on situation. This reactor, like its previous iteration also works in conjunction to form bigger, more efficient Micro-RTs to provide better power distribution and powering new formed modules. With this increased power, Iron Man was able to send Cull Obsidian flying in New York with his brand new energy displacer cannons.
The New Element Arc Reactor Mark VI
The most advanced and final model of arc reactor designed by Tony Stark. This latest reactor combines features from both the Mark V reactor and the Mark III used on the Mark XLV (while retaining Mark Vs visual design), as well as allowing the reactor be supercharged without being damaged in the process. This reactor housed the Mark LXXXV and it's modules. This power source allowed Iron Man to kill Outriders in one blast each. Smaller variant of this reactor model also powers the Mark XLIX (Rescue Mark I) armor, a modified version of this reactor with a different shape also powers the Iron Patriot Mark II armor, but neither of the suits feature nano-particle storage or module formation/augmentation features. This Reactor variant is slightly larger than the Mark V.
Tony uses the new arc reactor to power his Mark II and Mark III suits, but has it stolen by Obadiah Stane to power his own Iron Monger suit. Tony reclaims his Mark I reactor and uses it to power the Mark III suit in the battle against Iron Monger.
The reactor isn't powerful enough to power the suit for long so Tony has Pepper overload the Large Arc Reactor, creating an energy surge and kick that kills Stane and destroys the Mark II reactor while the Mark I runs out of power. Tony later creates the Mark III reactor to replace his destroyed Mark II.
The palladium in the reactor is slowly poisoning Tony to death. He has modified Mark II armor as a integrated reactor testbed, allowing James Rhodes to steal the Mark II suit and turn it into War Machine. He later creates a new reactor made of a new element that no longer poisons him and greatly increases the power he has access to. Specifically for this purpose, he modifies the Mark VI design to suit advantage of the new reactor with greater power for increased capability. Ivan Vanko also creates his own arc reactors to power his whips and armor which he knows how to do as his father was Howard Stark's partner in creating blueprints of the first arc reactor.
Tony creates a bigger version of the New Element Arc Reactor to power Stark Tower. Loki later uses the reactor's power to create a wormhole using a special device in conjunction with the Tesseract. J.A.R.V.I.S. shuts down the reactor but not before the device became self-sufficient.
During the final battle, Pepper takes down the Mark VIII suit by punching through its arc reactor. The arc reactors powering the Iron Legion are destroyed when J.A.R.V.I.S. self-destructs the suits. Tony later has surgery to remove remaining shrapnel from his chest with doctors using the arc reactor powered electro-magnet catching the pieces once they are removed. Afterward, as the arc reactor is no longer needed to power the electro-magnet, Tony pitches it into the sea.
- The Arc Reactor is based on the reactor of the same name in the comics, both having almost the same appearance and functionality.
- In the Iron Man 2 novelization, the element created for the new arc reactor is referred to as vibranium. However, in the movie continuity, vibranium is a metal compound from the region of Wakanda that was used to create Captain America's shield; it was not an element created by Howard Stark and used in the arc reactor. Therefore, while he would not have continued to become sicker once the palladium reactor was removed, a multi-month course of treatment should have been needed to remove the material already in his body.
- The Arc Reactor bears a striking resemblance to the Guyver Unit, from the 1980s manga and anime series Bio Booster Armor Guyver. The Arc Reactor debuted in the 2000s, some two decades after Guyver.
- The way the Arc Reactor appears as a glowing orb on Iron Man's chest also bears a resemblance to the superhero Ultraman, who also had a glowing orb in his chest since the 1966 TV show. While there wasn't a glowing orb on Iron Man's chest until the 2000s.