Sometimes though...

Both cannot kill the protagonist even if they are more powerful than him and both try to take him to the dark side in the 5th

And both are white

And something less than the normal human ( Palpatine has 9,5 fingers )

And they somehow they returned

And they returned once by another person ( Tom Riddle, Snoke)

And if we agree with the theories of how Snoke was made, they got something by the protagonists on them

But take an upvote