A person who manipulates or controls someone else, especially to achieve their own goals, often from behind the scenes.
From the 1894 novel 'Trilby' by George du Maurier, where Svengali is a sinister music teacher who hypnotizes and controls the titular character. The term entered English as a generic word for any manipulator.
It's remarkable that a fictional villain from a Victorian novel gave us a permanent vocabulary word—Svengali is to 'puppet master' what 'Sherlock Holmes' is to 'detective,' showing how powerful literature can literally reshape how we talk.
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