Hal Jordan has faced a lot of villains, but his arch nemesis is one he used to call friend. Thal Sinestro was the Green Lantern of Sector 1417 and when Jordan first became a Green Lantern, Sinestro was his mentor, taking him under his wing. However, Sinestro wasn't all he was cracked to be- he bragged that his sector was the safest in the universe but the reason behind that was because he ran it like a fascist dictatorship.
He would be removed from the Corps and forge a power ring of his own- one that worked on fear. Wielding this ring, Sinestro would spread his own brand of order throughout the universe with Jordan and the other Green Lanterns always standing in his way. This list is going to look at the worst things Sinestro has done over the years.
10 Killed A Green Lantern Corp. Member To Keep His Ring
Sinestro started out an anthropologist on Korugar. One day, an injured Green Lantern crashed into a dig site Sinestro was working. The Green Lantern gave Sinestro his ring and Sinestro used it to fight off the Lantern's pursuer- a Weaponer of Qward. In a bit of a twist, the Lantern survived his injuries... but didn't survive Sinestro. Not wanting to give the ring back when the Lantern asked, Sinestro killed him.
The Corps never found out about this and it would be the first step Sinestro took down the villainous path.
9 Helping Kill The Freedom Fighters
In the run up to Infinite Crisis, the villains of the DC Universe got organized, working together to take on the heroes. At one point, the heroic team known as the Freedom Fighters were investigating them and a group of villains, including Sinestro, attacked the group.
The resulting battle was terribly brutal and killed just about every member of the team, except Uncle Sam and Damage. Sinestro personally killed Black Condor, which is why this one ranks pretty low because Black Condor is only one man.
8 Creating His Yellow Ring
After being forced from the Green Lantern Corps, Sinestro was determined to get revenge as well as spread his perverted version of order throughout the universe. His journey would take him to his old enemies on Qward, where he would forge his yellow power ring.
While this doesn't seem like something that should be on a list of worst things someone has ever done, without this ring, millions of beings throughout the universe would have been better off. Sinestro used his ring to kill countless people and put his evil schemes into place.
7 Unleashing Superboy-Prime
This one wasn't something Sinestro personally did, but it was done on his orders. After being apprehended at the end of Infinite Crisis, Superboy-Prime was placed in a cell orbiting a red star by the Guardians near Oa. When the Sinestro Corps attacked Oa in the opening salvo of the Sinestro Corps War, they freed the mad Kryptonian.
Superboy-Prime is one of the most dangerous and unpredictable beings in the universe and Sinestro decided that unleashing him again was a good idea, all so his new Corps could be more powerful.
6 Making A Deal With The Anti-Monitor
After battling a returned Hal Jordan, Sinestro returned to the antimatter universe. While there, he made a deal with the greatest evil the DC Universe had ever known- the Anti-Monitor. The two vowed to work together to spread fear throughout the universe and so the seeds were planted for the Sinestro Corps.
The Anti-Monitor is responsible for an incalculable amount of deaths throughout the Multiverse and Sinestro, a guy who liked to pretend he was all about order, teamed up with him. That's really, really bad.
5 Mass Kidnapping
In one of his initial clashes with Hal Jordan, Sinestro used a device to kidnap a hundred thousand people and imprison them in the antimatter universe of Qward. He used them to try and blackmail Hal Jordan, threatening to kill all hundred thousand of them.
Kidnapping a hundred thousand people to use as blackmail fodder is easily one of the most evil things any villain has ever done. For Sinestro, it was just one of the first terribly evil things he's ever done.
4 Flying In A Fascist Space Sector
When Sinestro was the Green Lantern of Sector 1417, it was the safest sector in the universe, a model for all the other Green Lanterns to aspire to. However, Sinestro never let other Lanterns into his sector to study his methods and no one questioned this at all. The Silver Age was a different time, folks.
Eventually, it was revealed that Sinestro was running his sector like a fascist dictatorship with himself as the dictator, using fear to keep the people in line. This was a big no-no as far as the Guardians were concerned and caused them to kick him out of the Corps.
3 The Last Temptation Of Hal Jordan
After one of his defeats, Sinestro was sentenced to death by the Guardians. However, he was able to send his spirit into the Central Power Battery and there discovered the reason for the so-called "yellow flaw" in Green Lantern rings- the fear entity known as Parallax.
He would direct Parallax to possess Hal Jordan, slowly breaking down the Green Lantern. After the destruction of his home, Coast City, Parallax was able to take complete control of Jordan. Jordan would then go on a rampage, killing thousands, and it was all because of Sinestro.
2 Creation Of The Sinestro Corps
Sinestro was always ostensibly about spreading order throughout the universe and decided the best way to do that was through fear. After making a deal with the Anti-Monitor, Sinestro began to comb the universe, trying to find beings who were capable of instilling great fear into those around them. He would gather these beings together, giving them yellow power rings. The Sinestro Corps was born.
The Sinestro Corps would be responsible for countless deaths throughout the universe, killing not just Green Lanterns, but also innocent people. Sinestro populated it with the most terrible beings in the universe, gave them power, and unleashed them. It doesn't get much more evil than that.
1 Genocide
Remember how the Guardians sentenced Sinestro to death? Here's why- genocide. During one of his imprisonments on Oa, Sinestro was able to manipulate the Mad God of Sector 3600, freeing himself, and gaining near unlimited power in the process. He would use this power to destroy multiple star systems, murdering all the inhabitants within them.
There are few villains out there who have committed genocide on the scale that Sinestro has. Whole planets have been destroyed by him and billions of lives lost. It doesn't get much worse than that.