The American writer of speculative fiction Fred Saberhagen, who has died aged 77 of prostate cancer, was best known for his Berserker series, in which self-replicating robotic probes, a doomsday device left over from a vast interstellar conflict, are programmed to destroy all organic life. In the cold-war era of mutually assured destruction, the Berserker series touched a chord, and its post-apocalyptic setting would be reflected in much science fiction.

The series was an obvious influence on television's Star Trek, in an episode called The Doomsday Machine, on films such as Screamers or The Terminator, and in countless novels and stories. Eventually, Saberhagen registered Berserker as a trademark to stop more imitators of his work. The series would run to 18 titles over almost 40 years, including Berserker Base (1985), in which Saberhagen wrote a story arc and then filled in between segments written by guest authors by way of tribute.

Although never a celebrity figure within the world of science fiction, Saberhagen was often ahead of trends that others made bigger, particularly with his 10-novel Dracula series, in which the vampire count was the hero. His inspiration came while re-reading Bram Stoker's original and realising Dracula's presence was largely offstage. Saberhagen wondered what the vampire himself would be thinking about the whole business. The first in the series, The Dracula Tape (1975), predated Anne Rice's Interview With a Vampire by a year.

Saberhagen would later team Dracula with historical figures such as Napoleon, and fictional ones such as Sherlock Holmes, but his biggest success came with the novelisation of Francis Ford Coppola's 1992 movie, Dracula. "It was just eight weeks of well-paid fun," he said, "but nothing to do with my own books."

Saberhagen was born in Chicago. After serving in the US air force, he worked as a civilian technician for it. He was 30 before he sold his first story, Volume Paa-Pyx, which appeared in Galaxy magazine in 1961. His first novel, The Golden People, was published in 1964, and the first Berserker book, a collection of stories, in 1967. At that point, Saberhagen took a job with the Encyclopaedia Britannica, writing and editing entries on science and technology. Science fiction writers will argue interminably about the definition of their genre; in his position with Britannica, Saberhagen wound up writing the encyclopaedia's definition of it.

In 1968 The Broken Lands began a trilogy of fantasy novels finished in 1973 and gathered as The Empire of the East. He left Britannica in 1973 to write full time, moving to Albuquerque, New Mexico. Along with his series novels - which made up two thirds of his 65 books - his best work includes the time-travel novel The Veils of Azlaroc (1978) and two collaborations with his New Mexico neighbour Roger Zelazny, Coils (1981) and The Black Throne (1990).

With the Swords and Lost Swords series, Saberhagen returned to the world of the Empire of the East, in 11 novels about "swords of power" in a far future where sorcery works. In the last of the series, The Book of Ardneh (2006), Saberhagen revealed that the swords themselves were creations of another post-apocalyptic computer, echoing the world of the Berserkers as well.

Saberhagen characterised his fiction as "efforts to define the boundaries of humanity", and his most anthologised story, What Do You Want Me to Do to Prove I'm Human Stop reflected that goal. In 2002 he began another series, The Book of the Gods, in which he retold Greek myths, dealing with gods and heroes as he did vampires, wrestling with the concept of what exactly separates them from humans.

Soft-spoken and popular with fellow authors and fans, Saberhagen is survived by his wife, the writer Joan Spicci Saberhagen, and three children.

· Fred Thomas Saberhagen, writer, born May 18 1930; died June 29 2007