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Ruk was an android constructed at least one million years ago by the Old Ones on Exo III and discovered by Roger Korby in 2261. (TOS episode: "What Are Little Girls Made Of?") He was created in response to The One's sapping of the Old Ones' primary star. The Old Ones placed Ruk on stand-by, for approximately 500,000 years, when discovered by Doctors Korby and Brown. (TNG novel: Q-Strike)
Ruk article at Memory Alpha, the wiki for canon Star Trek.