Malkus the Mighty was a legendary tyrannical Zalkatian leader of the Zalkat Union. He ruled for a thousand years, with the help of four powerful weapons, later dubbed "the Malkus Artifacts." He was eventually overthrown and killed, but he was able to impress pieces of his consciousness into three of the Artifacts, and his whole consciousness into the fourth, before they were separated and hidden across the galaxy. (ENT - The Brave and the Bold, Book One short story: "Prelude: Discovery")
In 2376, after some 90,000 years, the fourth Artifact was unearthed, and Malkus was able to exert his will upon all the minds that had previously been imprinted by the four devices, as well as the minds of the planet Narendra III. After a short battle between Malkus's thralls and the combined crews of the USS Enterprise-E and the IKS Gorkon, Malkus's control was broken, and his consciousness contained once again. (TNG - The Brave and the Bold, Book Two novella: The Final Artifact)
