Who is the greatest fictional villain of all time?

Moriarty

And why is it Sephiroth?

Skeletor?

Darth Vader

Define 'greatest'?
Most worlds dominated?
Most fatalities?
Quickest conquests?
Best layered plans?

I don’t do a lot of villainy stuff, but I would certainly second Moriarty and throw in Hannibal Lecter. I don’t think I’d wanna be neighbors with him.

No villain is great in my eyes, they're horrible, terrible people. However, Spider-Man turns dark and then overcomes his darjsidevand becomes good again. So he's my greatest villain.

Professor Moriarty is definitely in the running.

Melkor......aka Morgoth Bauglir

The Joker, of course

Silas Greenback

Mumra?

The Master from Doctor Who.