He was briefly active as a superhero called "The Adjuster".
The insurance company Walter used to work for took him and his co-workers to a team-building retreat in the mountains. When playing a game of capture-the-flag, he fell into a cave, where a pool of billions of small, living bugs called Prolatomebia volubilis covered him: connecting to him through telepathy, they turned into a suit, making his greatest wish of having superhero powers come true.
Upon his return to Old City, Walter began to listen to police radio and intervened in crime and emergency situations as a superhero called "The Adjuster." This went well for a time, until he interfered with the Sanctuary Network's work by "saving" an abnormal they tried to protect. They eventually found a way to get him and found out his secret. Dr. Helen Magnus also discovered that the suit was slowly consuming him and would eventually kill him. They tried to get it off, but without success.
The Adjuster ended up helping Sanctuary in one more mission, assisting in the capture of an insectoid abnormal that had hatched under the city. After that, the team prepared to kill the bugs in the suit to save his life. At that point, Walter was finally prepared to let the suit go, so it followed his wish and moved to a small container.
Walter returned to his normal life, but with a change of career: he became a successful comic book author, receiving a number of award nominations and selling the film rights for his first work: "The Adjuster."