Hactar was made by the Silastic Armorfiends and was the first computer whose individual components reflected the pattern of the whole, much like DNA in a biological organism. The Armourfiends ordered him to create an "Ultimate Weapon;" Hactar took the request literally and built a supernova bomb which could connect every major sun in the Universe through hyperspace, resulting in every star going supernova. Deciding that he could find no circumstance where such a bomb would be justified, Hactar built a small defect into it. After discovering the defect, the Armourfiends pulverize Hactar.
Even in his pulverized state as floating atoms, Hactar was still very powerful. He moved and recombined to become a dark cloud surrounding Krikkit, which isolated the inhabitants. Deciding that the decision not to destroy the Universe was not his to make, he used his influence to make them build their first spaceship and discover the Universe; he then manipulated them into the same rage which the Armourfiends possessed, urging them to destroy all other life. Hactar was seen to enjoy manipulating others into becoming aggressive and murderous.
After an incredibly long war, Krikkit was banished to an envelope of "Slo-Time." After his scheme failed, Hactar slipped the cricket-ball-shaped supernova bomb to Arthur Dent, who then accidentally saved the Universe again by being an abysmal cricket bowler.
When facing interrogation, Hactar manipulated the environment to make his surroundings that of a psychiatrist's office. He made himself sit on a five-foot couch, which was remarkable because he himself was a thousand miles long. The computer defended his actions as simply fulfilling his original function, as well as revenge on the Universe for the æons of suffering he had endured as a result of his original decision.