Formerly a U.S. soldier who became a mercenary specializing in covert operations, Simon Maddicks was hired by the Brand Corporation, a subsidiary of the Roxxon Oil Company, who subjected him to bionic treatments and gave him the costumed identity of the Killer Shrike. Roxxon Oil had Shrike infiltrate a rival shadow organization, the Conspiracy, who continued to make large purchases from the Brand Corp. For reasons of their own, the Conspiracy was interested in capturing the monster called Goram, ordering the Shrike to do so and bringing him into conflict with the monster-hunter Bloodstone. Bloodstone defeated his opponent by knocking his power gauntlets together, shorting them out and leaving him comatose in the backlash.
The Shrike survived his coma but with little memory beyond the recent past. The Brand’s Modular Man contacted Shrike, offering him information about his past in an exchange for help in a scheme to enhance the Modular Man's own superpowers. This led them both to battle [[Spider-Man (Peter Parker)|Spider-Man and the Beast, and the Shrike was downed. Using the Shrike’s own wrist blasters, the Beast fired upon the Modular Man, defeating the villain. Unfortunately, the Modular Man may have been killed before he could make good on his promise to the Killer Shrike.
Escaping policy custody, the Shrike was again contacted by agents of the Brand Corporation, who helped restore his memory and set him up with an alias Harold Simmons, bodyguard for the Brand president, James Melvin. Melvin, however, had once left a Brand scientist, Jackson Arvad, to die during an accident in his laboratory. Arvad had actually become a being of pure energy, Will-O'-The-Wisp, and later returned to exact revenge. The Wisp managed to enter and control the Killer Shrike’s battlesuit, using the Shrike as a puppet to kidnap Dr. Marla Madison (then, love interest of J. Jonah Jameson and to bring her to his old lab. There, the Shrike/Wisp was confronted by Jameson and Spider-Man, but the Will-O'-The-Wisp regained his corporeal form, destroyed the laboratory, and escaped. Eventually, when the Brand Corporation was dissolved, the Killer Shrike became a free agent once more.
The Shrike sought out the Tinkerer for an upgrade to his power systems, using them to rob an armored car but being forced to flee by the timely arrival of Spider-Man. Spider-Man also happened upon the Tinkerer just as the Shrike was seeking him out to threaten him since he didn’t get the money from the robbery. The Tinkerer, however, merely activated a fail-safe in the Shrike’s system, rendering the villain unconscious after an overload of power. The Tinkerer escaped, but Spider-Man was able to remand the Shrike to police custody.
The Shrike continued to plague the life of Spider-Man, but also ran afoul of Moon Knight and She-Hulk on separate occasions. When attending a weapons expo run by A.I.M., the Shrike briefly battled Captain America and his allies.
Perhaps realizing that a solo career had proven less effective, he joined the Air Force, an elite team of mercenaries. The team, led by Cardinal, clashed with the New Warriors during the course of their missions and were usually defeated. Later, the team was tricked by the Warriors into participating in African relief efforts. During their time in Africa, however, they were opposed by the radical right-wing organization Undertow and its superhuman Soldiers of Misfortune. Many of the Air Force were killed or wounded, requiring the assistance of the New Warriors to help rescue their teammates. The Air Force have yet to reassemble after that debacle. The Shrike was again part of a team, however, later joining agents of the Master of the World in his fight against the Heroes for Hire, only to be imprisoned once more.
After a particularly one-sided battle against the Avengers, the Killer Shrike was arrested and placed into S.H.I.E.L.D. custody. The organization had determined that the Shrike must be getting bankrolled in order to always fund his equipment. The Shrike could only point to the Tinkerer as his arms man, and so he reluctantly agreed to a plea bargain in which he would help S.H.I.E.L.D. in a sting operation to find a true mastermind. Unfortunately, Simon Maddicks only got to the front door, as he fell victim to the Tinkerer’s trap and was electrocuted. Pursuing other leads, S.H.I.E.L.D. discovered the Latverian Prime Minister Lucia von Bardas was behind the funding of the Shrike and numerous other supervillains by way of the Tinkerer.
Although he was initially pronounced dead at the scene, the Killer Shrike recently reappeared. He was among those villains rounded up by the Thunderbolts, who were working on behalf the United States government to capture super-villains in the wake of the Civil War|Superhuman Registration Act. Like the other captured villains, the Killer Shrike was offered a choice to go to prison or to register himself with the SHRA and join the team, and he opted for the latter.
Recently, he was killed in the hospital by the Black Spectre.