Perhaps you are referring to Aulë, because both Sauron and Curumo were in the beginning maiar of Aulë that later turned into evil.
Or Melkor can be an answer because it could be that Melkor instructed some of the maiar that entered into his service. He could have instructed the 7 balrogs perhaps.
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"Alas, poor Yorick! I knew him, Horatio; a fellow of infinite jest, of most excellent fancy."
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