The Berserker series is a series of space opera science fiction short stories and novels by Fred Saberhagen, in which robotic self-replicating machines strive to destroy all life.

These Berserkers, named after the human berserker warriors of Norse legend, are doomsday weapons left over from an interstellar war between two races of extraterrestrials. They all have machine intelligence, and their sizes range from that of an asteroid, in the case of an automated repair and construction base, down to human size (and shape) or smaller. The Berserkers' bases are capable of manufacturing more and deadlier Berserkers as the need arises. The Berserker hypothesis, formed as a possible solution to the Fermi paradox, takes its name from the series.

The Berserker stories (published as novels and short stories) depict the fight between Berserkers and the sentient species of the Milky Way Galaxy: Homo sapiens (referred to as "Earth-descended" or "ED" humans, or as "Solarians") which is the only sentient species aggressive enough to counter Berserkers.

The first story, "Without a Thought" (originally published as "Fortress Ship")^[1] (1963), is a puzzle story, whose protagonist must find a way to simulate intelligence to fool an enemy trying to determine whether there was any conscious being present in a spaceship.

Saberhagen came up with the Berserker as the rationale for the story on the spur of the moment, but the basic concept was so fruitful, with so many possible ramifications, that he used it as the basis of many stories. A common theme in the stories is of how the apparent weaknesses and inconsistencies of living beings are actually the strengths that bring about the killer machines' eventual defeat.

The second story, "Goodlife" (1963), introduces human traitors or collaborators who cooperate with the Berserker machines to stay alive for a little longer.

The original Berserkers were designed and built as an ultimate weapon, by a race now known only as the Builders, to wipe out their rivals, the Red Race, in a war which took place at a time corresponding to Earth's Paleolithic era. The Builders failed to ensure their own immunity from Berserker attack, or they lost those safeguards through an unknown malfunction that changed the Berserker programming, and they were exterminated by their own creation very shortly after the demise of the Red Race. The Berserkers then set out across the galaxy to fulfill their core programmed imperative, which is now, simply, to destroy all life wherever they can find it.

A similar premise, though on a much smaller scale, was previously introduced by Walter M. Miller, Jr., in the 1954 short story "I Made You", described by reviewer N. Samuelson as "A pure 'sorcerer’s apprentice' sketch, about a war machine on the moon which kills anyone who comes within its range, including one of its programmers, because its control circuits are damaged."^[2]

The Berserker stories features many different characters originating from many different species, human and alien. These include:

• A board game based on the series was produced by Flying Buffalo Inc in 1982.^[5]
• A comic book adaptation is being created by Fan-Atic Press.^[6]
• The play-by-mail game Starweb uses the term "Berserker" with permission of Fred Saberhagen; Saberhagen returned the favor by using a fictionalized Starweb game as a backdrop for the novel Octagon.^[7]

Other examples of science fiction stories containing replicators bent on the destruction of organic life include:

• Cylons, robotic antagonists bent on destroying all humankind.
• "The Doomsday Machine", a Star Trek episode about a planet-eating machine from another galaxy.
• the Festival, a civilization of uploaded minds with strange designs on Humanity, in Singularity Sky by Charles Stross.
• the Hypotheticals, intelligent Von Neumann machines with strange designs on Earth, in Spin by Robert Charles Wilson, although the Hypothetical's goal is to save Mankind and other sentient species, not destroy them.
• the Inhibitors, in the fiction of Alastair Reynolds: a formerly organic race, completely converted over to machine form, who are non-sapient, and describe themselves as "post-intelligent".
• the Killers, a civilization of self-replicating machines designed to destroy any potential threat to their (possibly long-dead) creators, in The Forge of God and sequel Anvil of Stars by Greg Bear.
• Reapers, machine intelligences bent on the destruction of organic life, in Mass Effect.
• Necrons, an ancient race of skeleton-like robots in Warhammer 40,000.
• Skynet, an artificial intelligence bent on the destruction of mankind, and its agents the Terminators, in the movie The Terminator and its sequels.
• the Xymos Nanoswarms in Prey by Michael Crichton.
• the (!*!*!), a machine intelligence/civilization bent on the extermination of organic life, from the Bolo universe stories about a fictional type of artificially intelligent super-heavy tank.
• the Replicators of the Stargate universe
• the Claws, self-replicating, self-improving killer robots from the Philip K. Dick story Second Variety, which were designed by the United Nations following a devastating nuclear war with Russia, and intended to kill any human not wearing a special wristband. The book was adapted into the 1995 film Screamers
• the Artificial Machine Intelligence that evolved from Starfleet's Section 31 Threat Analysis AI "Control" destined to eradicate all organic life in Star Trek: Discovery. The cyclical rise and defeat of similar past and future Genocidal AI's later becomes a key plot point in Star Trek: Picard.
• the machines from the board game Legions of Steel. They emerge at the edge of the galaxy, take over planets on which they create factories to replicate themselves and mount attacks on the factions of the Milky Way.
• Berzerk (1981) by Stern Electronics and Robotron: 2084 (1982) by Williams Electronics Games take cues from the novels as players fight robots bent on destroying humanity.

• Starweb, a game featuring Saberhagen's Berserkers
• "Second Variety"—short story by Philip K. Dick. Self replicating machines have devastated both sides of a world war between East and West.
• List of works by Fred Saberhagen