General Old Iron is a giant humanoid spirit who appeared as the main antagonist of The Rift, the third comic trilogy taking place between Avatar: The Last Airbender and The Legend of Korra.
During the era of Raava, General Old Iron was a very close friend and protector of Lady Tienhai. But a tribe of humans made their home on the seashore without the spirit's permission, causing Old Iron to plot their extermination. He was stopped, however, by Lady Tienhai, who became fascinated with the humans. This caused one of the titular rifts between the two spirits, causing Old Iron to leave.
Centuries later, Old Iron felt Lady Tienhai drawing her last breath. Devastated by her death, Old Iron blamed the humans for her death, and marched towards the mainland with the intention of wiping them all out from existence. He battled Avatar Yangchen throughout the night, but she eventually got through to him. He told her his backstory of who he was and why he was angry, and though she listened, he did not intend to stop. They battled once again after he directly attacked the village people, but this time, Yangchen made an agreement with Old Iron, one that would be upheld ritually, halting Old Iron's vengeance.
However, by 102 AG, Team Avatar and a few Air Acolytes had found his armor near the factory that had been built in its place. When his armor was touched, Old Iron rose from the sea and took it back, dragging Satoru, Sokka, and Loban with him as he stormed the city. Upon seeing the deal he made with Yangchen was broken, he once more threatened to wipe humans out of existence. Yangchen's successor, Avatar Aang, battled Old Iron. Both were matched in power until Toph and her student metalbent his armor off, leaving a hole for Aang to attack with the power of all four elements. Old Iron was defeated, but Aang still tried to convince him that humans and spirits could co-exist. Undeterred, Old Iron stated that whenever there was a rift between humans and spirits, Aang would always side with the humans. Convinced that humans would always seek dominance over spirits and that there was no place for him in the world, Old Iron retreated to the sea for good.