a person who dominates or manipulates another, esp. with evil intentions
See Svengali in American Heritage Dictionary 4
Sven·ga·li
nounpl.Sven·ga·lis
A person who, with evil intent, tries to persuade another to do what is desired: “a crafty Svengali who lures talented people with grand promises yet gives them little lasting operational authority”(Chris Welles).
Origin: After Svengali, the hypnotist villain in the novel Trilby by George du Maurier.