The Zodiac Killer is an unidentified serial killer who operated in Northern California during the late 1960s and early 1970s. The killer is known for committing at least five murders between 1968 and 1969, targeting young couples. The case gained notoriety due to the killer's taunting letters sent to local newspapers, which included cryptograms and threats. Despite extensive investigations by law enforcement and amateur sleuths, the Zodiac Killer was never caught. The case remains one of the most famous unsolved criminal mysteries in American history, inspiring numerous books, films, and documentaries that explore the killer's identity and motives.