Flexible and imaginative, Hactar was the first computer whose individual components reflected the pattern of the whole, much like DNA in a biological organism. Hactar is made by the Silastic Armourfiends, who ask for an "Ultimate Weapon". Hactar, taking the request literally, builds a supernova bomb which would connect every major sun in the universe through hyperspace, thus causing every star to go supernova. Deciding that he could find no circumstance where such a bomb would be justified, Hactar builds a small defect into it. After discovering the defect, the Armourfiends pulverize Hactar.

Over æons Hactar moves and recombines to become a dark cloud surrounding Krikkit, isolating the inhabitants. Deciding that the decision not to destroy the universe was not his to make, he uses his influence to make them build their first space ship and discover the universe; he then manipulates them into the same rage which the Armourfiends possessed, urging that they destroy all other life.

After an incredibly long and bloody galactic war, banishes Krikkit to an envelope of "Slo-Time" to be released after the rest of the universe ends. After his scheme fails, Hactar slips the cricket-ball-shaped supernova bomb to Arthur Dent, who then accidentally saves the Universe again by being an abysmal cricket bowler.