The Zodiac Killer, or simply Zodiac or the Zodiac, is the pseudonym of an unidentified serial killer who operated in Northern California in the late 1960s.The killer originated the name himself in a series of taunting letters and cards that he mailed to regional newspapers, threatening killing sprees and bombings if they were not printed. Some of these letters included cryptograms, or ciphers, in which the killer claimed that he was collecting his victims as slaves for the afterlife.