This was a very difficult list to make. There are so many great villains to choose from and some are arguably better than others. I've spent a life time collecting comics and researching each hero and villain. Throughout the course of my collection and research, I've discovered many great villains who are underestimated and overestimated. In my previous list of 10 greatest superheroes, I gave you my list and why. Because there are so many great villains it's hard to choose just 10, so I thought i'd up the anty.
So what is a villain? The simplest answer is, it's someone who battles the heroes. But that could be any number of people, other superheroes, the media, the government, a God, GOD himself etc. etc. etc. So I had to narrow down the criteria. A villain is someone who can't be easily reasoned with, someone who will kill and is capable of killing, someone who is quite possibly soul less.
20. Lex Luthor

From his beginnings as a mad scientist to becoming Superman's arch enemy as a billionaire crime lord, Luthor has proven essential to the DC Universe. Luthor's hunger for power can never be filled.
19. Death Storm
The only black lantern to "survive" the Blackest night. I doubt even the destruction of the Anti-Monitor can keep this villain down.
18. The Borg
Resistance in futile. The borg aren't evil, but they plan to assimilate the entire universe.
17. Ultron
Emotionless, soulless, and powerful. Ultron wants only 1 thing... The Rise of the Machines.
16. Mongul II
This tyrant is probably one of the fiercest foes in the DCU, Killing his own sister for showing weakness and pulling Arkillo's tongue completely out of his mouth and making him wear it. Mongul II ends up at number 16 on our countdown.
15. Black Hand
This once petty criminal who took the life of his entire family, and created his costume out of a body bag has become one of the darkest villains in the DCU. Death in carnate, Black hand wants only one thing... EVERYTHING DIES!
14. Major Force
This once hero and veteran raped and killed an entire village taking pride in his work. Tortured and stuffed Green Lantern's girl friend and stuffed her remains in a refrigerator. The only thing that makes him scarier, is his atomic power.
13. General Zod
Three words... "KNEEL BEFORE ZOD!"
These three words have become iconic in pop culture. Zod will stop at nothing to rule and seek vengeance on the son of his jailer.
12. Eclipso
The former spirit of God's wrath before the Spectre, Eclipso has the ability to possess anyone and multiple people. Pure evil, he's no longer God's wrath but rather Wrath incarnate.
11. Darkseid
A God who killed his own mother, Darkseid fears only one thing... DOOMSDAY.
10. Apocalypse
Thousands of years old, this once slave learned from his former master that only the strong survive. Upon his master's death bed, The mutant slaughtered the master because he was no longer strong. A villain who's powers seem to be limitless in that with each new writer he seems to obtain new powers which makes him more and more difficult to defeat.
9. Violator
The Clown from Hell. Violator is a demonic soldier evil. His own brothers hate him, he desires the power of Spawn and wishes to rule hell himself. not even decapitation can keep this villain down.
8. Malebolgia
Many people consider the Devil himself as the ultimate super villain but after 100+ issues he was killed by Spawn. which is why his rank as world's greatest super villain dropped to #7.
7. Parallax
The embodiment of fear, Parallax was able to posses Hal Jordan and remain hidden deep within in his psyche for years before it made it's presence known. Using Hal Jordan's pain to wipe out the entire Green Lantern Corps Parallax's ultimate goal is to spread fear throughout the universe like wild fire.
6. Onslaught
He all but wiped out the Marvel Universe. Need I say more?
5. Henshaw The Cyborg Superman
A former scientist and pioneer in the Challengers of the Unknown. Hank Henshaw wants only 1 thing, his own death, and he'll destroy the entire universe in order to accomplish that goal.
4. Doomsday
The Destroyer of worlds. Created centuries ago on a primitive Krypton through years of forced evolution and cloning. His violent birth forged a creature that was relentless and unstoppable. The only being to actually kill Superman, Doomsday is a force that haunts every waking minute of the man of steel's life.
3. Carnage
Serial killer Cletus Cassidy is a threat to anyone in his human form, but went joined by the symbiote he's far deadlier. As a child he killed his grandmother by pushing her down a flight of stairs, and cooked the family cat in the oven. No Rules except CARNAGE RULES!
2. The Joker
Diagnosed in Arkham as Supersane, Joker is a rare villain in that he's not insane nor is does he want power. Joker's only plan is to bring as much havoc as possible. He killed Jason Todd, Molested and crippled Barbara Gordon, tortured the commissioner and even had his own face sliced off. Joker has only one rule, Batman doesn't die until Joker does.
1. The Guardians of the Universe

Emotionless, strong willed, immortal and many would say have a GOD complex. These little blue beings began by trying to bring peace to the universe by creating first the Manhunters, then the Green Lantern Corps. and finally the Third Army. They've taken the best of the Green Lanterns and turned them into mindless machines to act as internal affairs officers for their corps. They Refuse to accept emotion and cannot be reasoned with. The believe whole heartedly that they are the absolute of the universe; judge, jury and executioner. Their word is law and no one will stop what they set out to do. Even going as far as to lobotomize one of their own when he accepted emotion and reason. Their psychotic plans have included making one of their greatest enemies a once again member of their corps. They will stop at nothing in order to complete their plans even if that mean destroying a planet or entire galaxy. The Guardians of the Universe are the greatest villains of all time, they conceal themselves as protectors but these once Maltusians have become a threat to the entire universe.