Even though Tony Stark had his life-saving arc reactor removed in Iron Man 3, the MCU’s Iron Man still uses the technology during his later Marvel Studios appearances. After being taken captive by the Ten Rings in Iron Man, Stark equips himself with a miniaturized arc reactor, with the help of Ho Yinsen, which prevents pieces of metal shrapnel from making their way into Stark’s heart. This technology would later become the power source for Stark’s Iron Man armor in his initial MCU adventures, until Iron Man 3 saw the device become redundant after the shrapnel was surgically removed from Stark’s body.
While Stark went without an arc reactor during Avengers: Age of Ultron, Captain America: Civil War, and Spider-Man: Homecoming, Avengers: Infinity War saw Stark sporting a very different arc reactor. Stark’s first arc reactor had two purposes: to keep the shrapnel from entering his heart, and to power his suits, which is still essential for his activities as Iron Man in the wake of Iron Man 3. According to The Art of Avengers: Infinity War, Stark replaced the life-saving arc reactor with an “RT Unit” (which houses nanobots for Marvel Comics’ Mark 50 Bleeding Edge armor), so the role of the arc reactor after Iron Man 3 was changed significantly.
Iron Man’s Glowing Chest Plate Is Nanobot Housing After Iron Man 3, Not An Arc Reactor
Instead of functioning as a normal arc reactor, the chest-piece displayed in Avengers: Infinity War actually houses a collection of nano-particles, which allow Stark to suit-up effortlessly and in a matter of seconds, without the hassle of assembling clunky pieces of armor. This was most evident during the opening moments of Avengers: Infinity War, where Stark showed off his new technology to Doctor Strange, Wong, and Bruce Banner in the initial fight against Children of Thanos members Ebony Maw and Cull Obsidian.
Prior to this, it took Stark longer to assemble his suits, going to great lengths to make sure they were always within reach; he even stashed one inside his helicopter in Captain America: Civil War. However, he knew that threats, especially the one he had been dreading since 2012’s The Avengers, can come at any time, motivating him to keep a nanotech suit attached to his body at all times. Following his three-week ordeal in space after the lost battle against Thanos on Titan, this RT Unit also became an emotional metaphor for the broken relationship between Stark and Steve Rogers, a.k.a. Captain America, at the beginning of Avengers: Endgame.
Ironheart’s Suit Is Also Powered By An Arc Reactor
Phase 4’s Black Panther: Wakanda Forever showed that the Ironheart suits created by Riri Williams are similarly powered by arc reactors. Riri built her first suit on her own, a rather crude model that provided the most basic defense, firepower, and flight speed, though this demonstrated the first appearance of her unique heart-shaped arc reactor. Combined with Stark’s arc reactor technology, Riri then collaborated with Shuri, the MCU’s new Black Panther, using vibranium to create the Ironheart Mark II armor, which was strong enough to keep Namor’s forces occupied.
How Else The Arc Reactor Could Appear After Iron Man’s Death
Avengers: Endgame might have marked Tony Stark’s final adventure as the MCU’s Iron Man, but his legacy will live on thanks to his creativity and technological mind. Arc reactor technology will surely continue to be relevant to the MCU, as there are many narrative reasons why the arc reactor could become a key piece of technology again. Two of Marvel Studios’ upcoming projects are set to build on Tony Stark’s legacy by focusing on Iron Man-adjacent heroes. Ironheart and Armor Wars could both rely on Stark’s arc reactor as a narrative device, especially since the latter will explore what happens when Stark tech falls into the wrong hands.
Marvel Studios’ Armor Wars will focus on Don Cheadle’s James “Rhodey” Rhodes, a.k.a. War Machine. Since the Mark VI War Machine armor Rhodey wears during Avengers: Endgame is powered by an arc reactor, and the fact that Rhodey can’t walk without Stark tech, finding a new arc reactor could be a plot point that could have a surprising level of emotional depth. Iron Man 3 may have rendered the arc reactor redundant for Tony Stark, but the technology will also have a special place in MCU history, even if it doesn’t become a key piece of technology in the MCU’s future.