Iron Mask, a sinister blacksmith who wore an iron helmet and vest, built a reputation in the Old West as he seemed unkillable, no one knew about his iron vest, giving him an almost supernatural reputation. At some point, the Iron Mask robbed the home of a rancher named Mr. Thompson, whom the Mask severely beat for trying to resist him. Thompson had befriended Kid Colt, who decided to have vengeance on the Mask. That evening, the Mask robbed the payroll before it arrived in town. Colt tried to stop him, but his bullets were useless and the Mask knocked him unconscious. When Colt awoke he promised local authorities that he could bring in the Mask within one hour. He traveled to the blacksmith shop and found the Iron Mask there. This time, when he drew, he shot the Mask in the arm, causing him to drop his gun. Colt ripped open the Mask's shirt and revealed the vest that had protected him from gunfire, then ripped off the mask to reveal that the Mask was none other than the town's blacksmith himself.
Iron Mask proved to be a model prisoner and was soon allowed to work in the prison's metal shop. Before long he had recreated his mask, along with a full suit of bulletproof armor, making him invulnerable. He then proceeded to break out of the prison and resumed his career of robberies; he also vowed to get his revenge on Kid Colt for having gotten him locked away in the first place. 
Kid Colt was himself on the run from the law, but when the lawmen heard that the Iron Mask was loose, they left the Kid alone to deal with him. Colt tried to make a break for it but ran into the Mask by mistake. He tried to shoot him in the arm again, but this time it didn't work. Iron Mask then shot back and nearly killed Kid Colt, who fell from his horse. When he revived, Colt wanted to help bring in the Mask, but the lawmen refused; it wasn't until the sheriff was shot by the ricochet of his own bullet off of the Mask that he allowed Colt to be set free. When the Iron Mask saw that the Kid had survived, he forgot about robbing banks and pursued him. The Kid tried lassoing him, but Iron Mask snapped the rope. Then Colt took off on his horse, with the Iron Mask following right behind. Colt lead him through a lake, and when they got to the other side, the Mask realized that the water had rusted his armor, making him unable to move. Colt then stripped off his armor and returned him to the law, humiliated.
At some point, the Rawhide Kid sought out Sam Hawk, the famous marshall known as the Man-Hunter, to help him save Silvertown from the Iron Mask, who had once again escaped from prison. Hawk, though, arrested Rawhide instead, and put him in prison with Kid Colt who he had arrested earlier that same day. The two Kid's broke out of jail, however, to put a stop to the Iron Mask once again. They found that Sam Hawk and his men had engaged Iron Mask in Silvertown, but could not penetrate the Mask's armor. Rawhide and Kid Colt then came to the rescue with guns blazing, scattering the Mask's gang in the resulting confusion. The Iron Mask, however, strode towards the two Kids, intent on killing them both. Rawhide led him down the town's streets, right over a set of wooden planks. The planks collapsed under the weight of Mask's armor, and he fell into a pool of water. In danger of drowning, the Mask was forced to surrender.
Later, having escaped prison once again, the Iron Mask came up with a scheme to rob the town of Phoenix, Arizona, as its new governor was being sworn in. He enlisted three of Kid Colt's old foes Bennington Brown, Dr. Danger and the Fat Man, and the four men disguised themselves as circus performers, with the Iron Mask wearing the costume of a clown to hide his armor underneath. To their surprise, Kid Colt showed up in town seeking a pardon from the new governor. The Circus of Crime defeated him, winning the opportunity to perform at the governor's dance that evening in the process. At the dance, the men revealed their true identites and proceeded to rob the wealthy townspeople, but Kid Colt, having himself escaped from jail, arrived and defeated the Mask's cohorts. Iron Mask ran out of town into a cave but was knocked unconscious when he fell to the ground during a scuffle with the Kid.
For his next scheme, the Iron Mask re-enlisted Dr. Danger and the Fat Man, and recruited Hurricane, Rattler, the Red Raven, and the Living Totem in order to commit large crimes. This drew the attention of the Rawhide Kid, the Phantom Rider and the Two-Gun Kid. The heroes were then joined by the time-travelling West Coast Avengers, and with their help, were able to defeat the entire gang. Shocked by his gang's easy defeat, Iron Mask tried to run, but was caught by the Avenger Mockingbird, and was once again returned to prison.
Powers and Abilities
Iron Mask initially wore an iron mask and iron vest that made those sections of his body impervious to bullets. Later, he developed full body armor, making him immune to bullets all over his body
- The Iron Mask's real name was revealed in Avengers: Roll Call #1 as Don Hertz.