Not much is known about Darth Plagueis. One thing I know is that
Darth Plagueis's species was a Muun, but no one knows who his
master was
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Darth Plagueis' master's name was the Sith Lord Darth
Tenebrous.
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Darth Plagueis' master was Darth Tenebrous. He was a male Bith Dark Lord of the Sith and played a significant role in training and shaping Plagueis into a powerful Sith Lord.
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It was widely assumed that Palpatine's master was Darth
Plagueis.