No, it's not The Lizard. For as much as I love the character, I know he isn't a big enough threat. I look for certain things in "the greatest comic book villain ever". Those things are: Power, intelligence, threat level, sympathy to a certain degree. When I think of these things, only one villain comes to mind....
Dr.Doom
When I say Dr.Doom is a villain with sympathy, I'm talking about his past with his mother. But yet, he becomes one of the world's greatest genuises. After an accident in college that severely burned his face, Doom travels the world until collapsing on a Tibetan mountainside. A clan of monks rescued Doom, he then learned their disciplines and forged himself a suit of armor and a mask. After that, he became Dr.Doom and since then has taken on the likes of the Fantastic Four, Spider-Man, Silver Surfer, The Avengers, Iron Man and other different heroes in the Marvel Universe.
Now, when I talk of his accomplishments, I will go into different medias. So, as for Dr.Doom accomplishments goes, he has gone to different extremes. From stealing the powers of the Silver Surfer himself to also stealing the powers of Odin. He has become the biggest threat in the Marvel Universe. Those were just to name a couple. Now, I do understand that The Infinity Gauntlet uses Thanos to his full potentional and he wipse out most of the universe. But, I feel that even though The Infinity Gauntlet became the largest threat the universe has seen that they needed an object to do that. Not that I am bashing on that storyline because I think that storyline is epic. But, Dr.Doom uses his brain as a weapon along with his powers.
Famous storylines: Here I will show a couple of examples of good or even great Dr.Doom storylines.
Fantastic Four #67-70, Fantastic Four #500 "Unthinkable"
Doomquest
Emperor Doom
Fantastic Four #600-604 "Forever"
The biggest reason this is on the list is because of it's "Holy Shit" ending. Which is this
I think these are some pretty valid points on why Dr.Doom is the greatest comicbook villain ever. Agree? Disagree? Comment below and be respectful about it.