The unnamed fictional character most frequently referred to as The Man in Black is the main antagonist on the American ABC television series Lost. He appeared primarily as a cloud of black smoke until the final episode of season five where he appeared as a middle-aged man dressed in black. In season six, he primarily appeared in the physical form of John Locke. He exhibited the ability to "scan" the minds and memories of others, allowing him to confront characters such as Mr. Eko and Ben Linus, with "judgement", and to assume the forms and memories of the deceased, starting with the original Man in Black himself, his brother Jacob, or Christian Shephard, Yemi, Alex Rousseau, and Locke. According to Jacob, who explains this to Richard Alpert, it is the incarnation of evil, and its primary goal—to escape from the island—would be the "end of everything good".

John Locke is a fictional character played by Terry O'Quinn on the ABC television series Lost. He is named after the English philosopher of the same name. In 2007, O'Quinn won the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series for his portrayal of Locke.