Sinestro was once the most revered Green Lantern the Corps had ever known, before he became Hal Jordan's greatest enemy. In his attempt to bring order to the universe, Sinestro decided to impose a harsh totalitarian regime on the people of Korugar, but its citizens rebelled after Sinestro was absent for a long time. The Guardians -- the immortal beings who created the Green Lantern Corps -- found out about Sinestro's rule and he was cast out of the Green Lantern Corps for his attempt at a dictatorship on his home planet. He was banished to Qward, the anti-matter universe’s version of Oa. That's where the trouble really began.
Once on Qward, Sinestro showed no remorse for his actions. Instead, he felt betrayed by the Guardians and his hate for them grew. The Guardians hoped that by sending Sinestro to a planet of species that hated Green Lanterns, he would be humbled by the experience. Instead, he exploited the hatred that the Weaponers of Qward had for the Green Lanterns and the Guardians to have them make the infamous Yellow Lantern ring. This ring would lead to a devastating war that would ravage the universe. It was a weapon that had horrors hidden within, the extent of which have only recently been realized...
The yellow impurity of a Green Lantern’s ring was a mystery until Geoff Johns wrote an extensive mythology explaining its existence. Parallax is a parasitic being that has been around since the dawn of time, a sentient incarnation of fear who has gone from planet to planet making their populations go mad and destroy themselves. The danger it posed to the universe had made the Guardians intervene and trap it inside the Green Lantern’s Central Power Battery. Parallax remained dormant until Sinestro woke it up.
When Sinestro was imprisoned in the Green Lantern’s Central Power Battery for his galactic crimes, he tapped into the power of his yellow ring and woke Parallax since it was sourcing its power from the embodiment of fear. This partnership eventually led to Hal Jordan "murdering" Sinestro and destroying the Central Power Battery, along with even bigger horrors soon to come.
14 CAN PERFORM AUTOPSIES AND VIVISECTIONS
In Green Lanterns #23, Soranik Natu becomes suspicious of how Kyle Rayner is acting after the death of the villain Sarko. She wonders why he keeps interrogating her about her character and whether or not she shares similar perspectives to her father, Sinestro, about leadership. She goes to the morgue to find out information on Sarko and why Kyle is acting so weird. She performs an autopsy and projects instruments of yellow light to get to work.
It’s a small scene in Green Lanterns, but it displays both the the power and finesse of the yellow lantern rings if they are utilized by someone with the proper intelligence. She opens the body up to scan it for possible contagions or other causes of death that aren’t rooted in violence. It even tracks the DNA information of many of the Sinestro Corps, which leads to a shocking revelation for the young leader.
13 ANTI-MONITOR IS THE YELLOW LANTERNS’ GUARDIAN
When the Multiverse was recreated after Infinite Crisis, Anti-Monitor was reborn and he had started supporting Sinestro’s ideology at the time. He served as the “Guardian of Fear,” functioning in a similar way as the Green Lanterns’ Guardians of the Universe. The Manhunters rebuilt his body piece by piece and when he was fully assembled, he started recruiting villains like Superman Prime, Cyborg Superman, and a Parallax-possessed Kyle Rayner.
This team-up with the Sinestro Corps led to the slaughter of many Green Lanterns. He even experimented with various torture techniques on the entity known as Ion. When he landed on Earth with Sinestro, he started siphoning the positive matter from Earth, but was thwarted by an attack orchestrated by the Guardians of the Universe. They were a match for the villain, but only if they all attacked together.
12 SIPHONS GREEN LANTERN ENERGY
Sinestro’s Yellow Lantern ring does many of the things that the Green Lantern rings do, but they have some differences because the source of their power is different. Green Lantern rings have an unfortunate weakness to the color yellow in the emotional spectrum. It has to do with the yellow impurity that lied at the heart of all Green Lantern rings, which, as we mentioned earlier, had to do wth Parallax being imprisoned in the main battery.
Yellow Lantern rings have a similar recharge procedure to the Green Lantern rings these days, but originally, it was revealed that Sinestro's ring would absorb the power output from a Green Lantern's. It was a strategy largely used by Guy Gardner during his time with the ring (though less maliciously than Sinestro's use of the ability). This syphoning was adapted during the "Sinestro Corps War" storyline by the Corps' fleet of Manhunters. Speaking of which...
11 POWER BATTERIES IN MANHUNTERS
The Yellow Lantern rings have to be charged like the Green Lanterns’ power rings. The trick with these is that the Sinestro Corps had a really interesting place to put their Yellow Power Batteries. They would stuff them in the heads of Manhunters behind their faceplates. This, coupled with the fact that the yellow power batteries can drain the energy of a Green Lantern’s ring, meant that any unsuspecting Green Lantern wouldn’t even realize they were losing power until it was too late.
This extension of the original ring's power was utilized heavily throughout the Sinestro Corps War as it afforded the Yellow Lanterns an advantage over their green counterparts. The Manhunters also fought hard in battle, which made them formidable against any Green Lantern. While it proved to be a good strategy during the war, the Sinestro Corps eventually stopped using Manhunters to store their batteries.
10 REMOVAL OF LETHAL RESTRICTIONS ON GREEN POWER RINGS
In the beginning of the Sinestro Corps War, the Yellow Lanterns basically gave the Green Lantern Corps the beating of their lives. It was a time for war, but the Green Lanterns had restrictions set on their rings that would not allow them to fight fair. They couldn’t kill with the green power rings because they were programmed by the Guardians not to inflict that extreme kind of violence.
Sinestro exploited this weakness of the Green Lanterns’ rings and his Corps was winning the war that he had started. It wasn’t until the Guardians gave the okay for those bearing the green power rings to kill that the Green Lantern Corps started to win. While the Sinestro Corps started getting pummeled and losing the war, Sinestro didn’t mind: he ultimately wanted the Guardians to go back on the limitation, thus making him -- in his mind -- the greatest Lantern of all.
9 HOPE WEAKNESS
Instilling fear in others is the trait that all Yellow Lanterns must have before they enter the Sinestro Corps. It is how those who bear the rings are chosen. However, the Yellow Lanterns’ rings have a weakness that can disrupt and drain their power. Hope renders a Yellow Lantern ineffective because its existence is antithetical to the emotion of fear. Where there is hope, fear has no power.
This is explained by Saint Walker during the Rage of the Red Lantern Corps, while the events of Final Crisis were occurring. When the Blue Lanterns intend to free Sinestro, they fight against the Sinestro Corps, but it soon turns into a nothing fight as the Yellow Lanterns realize very quickly that their rings no longer wielded any power in the presence of the blue power rings.
8 PUTS WIELDERS INTO A COMA
When Sinestro found out what the Sinestro Corps had done to his home planet of Korugar by terrorizing its citizens for their own selfish gains, he sought Hal Jordan's help to liberate them. It's a moment of redemption for Sinestro as he dons the Green Lantern ring again. Sinestro tells Hal he created a failsafe in the Yellow Lantern Central Battery to shut it down, but he'd need to use a Green Lantern Power Battery to do it.
They execute their plan flawlessly, aside from a few complications (one of which was Hal getting sucked into the Yellow Lantern Central Battery), but Sinestro introduces a Green Lantern into the core of the Sinestro Corps' Central Battery. It depletes the power of the Yellow Lantern rings and knocks those wearing them unconscious. That's a pretty malicious failsafe.
7 CHARGES KRYPTONIANS
As most fans of Green Lantern know, the green light from their power rings can be used to harm Kryptonians if the wielder's willpower is strong enough. Not only that, but the ring can and has created artificial Kryptonite energy, though the strain to do so is great. It is one of the few vulnerabilities that Kryptonians have, but as they suffer at the light of a Green Lantern, they have something to gain from exposure to the light of a Yellow Lantern.
That's right! A Yellow Lantern can actually have the opposite effect on a Kryptonian or Daxamite. The light from their rings actually gives those two species a power boost as it can manifest its energies to replicate the radiation of a yellow sun. It makes them supercharged. It's what made Superman donning the Yellow Lantern ring in the recent Superman #30 even scarier.
6 USED TO BE INVISIBLE
The very first yellow power ring constructed by the Weaponers of Qward for Sinestro was a weapon that former Green Lantern Guy Gardner wanted. Gardner had lost his Green Lantern ring after fighting one on one with Hal Jordan for the right to be the protector of Earth's sector. He ended up losing the right to the sector and had to return his ring to the Corps.
This did not stop him from continuing to fight as a hero, but no matter how many times he attempted to reinvent himself, he needed to have a power ring. It was believed that Sinestro's yellow power ring was still on Qward, but when he and Lobo went to investigate they found out it was still on Oa. It was still on Sinestro's finger, but it was invisible even while Sinestro was "comatose." It eventually became visible and Gardner took it for himself.
5 BEGINNING OF A PROPHECY
When the Yellow Lantern ring was created, it set off a chain of events that played into a prophecy that would unite the Weaponers of Qward, Ranx the Sentient City, the Children of the White Lobe, and the Empire of the Tears against the Green Lantern Corps. Its existence, coupled with the established Sinestro Corps, started the beginning of the Blackest Night prophecy.
Then Manhunters with upgrades -- including Yellow Lantern Power Batteries in their heads -- started popping up throughout the universe, led by Cyborg Superman, who was eventually subdued and brought to the Guardians of the Universe on Oa. They interrogated him and he divulged his knowledge of the 52 parallel universes. He also revealed that if New Earth was destroyed, it would mean the end of the multiverse. It was all foretold in the forbidden chapter of cosmic revelations in the Book of Oa.
4 USED TO ENSLAVE WEAPONERS OF QWARD
When the Weaponers of Qward understood Sinestro's own hate for the Green Lantern Corps, they teamed up with him to bring death and desolation to the protectors of the universe. Sinestro asked them to fashion him a ring that would exceed the power of the Green Lantern Corps, while tapping into their greatest weakness. They did, and from that single seed, the Sinestro Corps was eventually born.
Unfortunately, Sinestro hadn't gotten over his totalitarian approach to enforcing rules and regulations among people he had control over. He used his new ring to enslave them. They made him the Yellow Lantern Central Battery and plenty of others rings, so that Sinestro could grow his own Corps to combat the Green Lanterns. It was a rough time for the creators of the Yellow Lantern rings that would eventually wreak havoc on the universe.
3 THE BOOK OF PARALLAX
The Book of Parallax was created to serve as the Yellow Lanterns' Book of Oa's equivalent. It had all the actions and perspectives of every Yellow Lantern recorded into it. The pages of the Book of Parallax gives any person who can read it any information they would need about the Sinestro Corps and anything a member of the Corps ever did, but it must be accessed through the use of a yellow power ring.
This is necessary as it translates the language of the book into something the wielder/reader can actually understand. It's pretty freaky to think there's a book out there that not only records every action you've ever committed, but also thoughts you may have had in the privacy of your own head. The Book of Parallaxhas since been rewritten onto the very skin and soul of its keeper, Lyssa Drak.
2 WORN BY BATMAN AND SCARECROW
Batman and Scarecrow have both been chosen by the Yellow Lantern ring in the past. During the Blackest Night event, Scarecrow was relieved to receive it because he hadn't felt fear for the longest time and gleefully follows Sinestro's orders afterward. He even tried to stand against the Black Lanterns ringless, hoping it would make his heart start racing, but he quickly realized the only thing he was scared of was Batman.
Before the Sinestro Corps War, Batman was also chosen by a Yellow Lantern ring when Sinestro sent them out to recruit members for his Corps. Batman was perfect for the ring as he could instill great fear in the criminal underworld of Gotham. However, his passing contact with Hal Jordan's Green Lantern ring and his willpower prevented it from bonding with him. This demonstrated that the Yellow Lantern rings don't just choose villains to wear them, but rather any practitioner of fear.
1 FEAR LODGE
Every member of the Sinestro Corps is chosen by a yellow ring for their ability to instill great fear in the people they come across. Batman and a few others notwithstanding, most Corps members are malicious creatures intent on wreaking havoc in the universe. However, before they are fully inducted, Sinestro Corps members must pass a rigorous process wherein they are subjected to psychological and physical reconditioning.
After a Yellow Lantern recruit is put through their training with Arkillo and Lyssa Drak, they must enter the Fear Lodge. They can only exit the Fear Lodge once they faced their greatest fears, or die in the process. Their yellow power ring was given just enough charge that it would spark up and give them their exit from the lodge. Unfortunately, not everyone survives the lodge as it's been recorded in the Book of Parallax by Drak that many never exit and either starve to death or commit suicide.