I was actually surprised that Lucas and the producers were being so secretive about Darth Sidious and his true identity in the first prequel. As early as 1997 action figures of the Emperor from Return of the Jedi
were marketed as "Emperor Palpatine, Galactic Ruler and Dark Lord of the Sith."
Sidious was a Sith Lord. He sounded just like Senator/Chancellor Palpatine
. They had the same nose, mouth and chin. Palpatine had actually been the actual name of the Emperor as far back as a comic book or strip around the beginning of the '80s although his name never made it on-screen until the prequels came along. The book or strip spoke of a girl or Imperial palace subject "who grew up at the feet of the Emperor Palpatine" on the capital planet of the Empire.