Thaal Sinestro is a fictional character, an alien supervillain in the DC Comics Universe. Created by John Broome and Gil Kane, Sinestro is the former mentor of Hal Jordan and the arch-nemesis of the entire Green Lantern Corps.
THE RING OF FEAR
The first yellow ring is acquired by Thaal Sinestro following his banishment to the antimatter universe of Qward, and could only be recharged by fighting a Green Lantern. After his imprisonment in the power battery his ring was taken by Guy Gardner who used it until it was destroyed by Parallax. Upon his return to life, Sinestro was seen wearing a new yellow power ring. Before he could be defeated Sinestro retreated to the anti-matter universe where he spent the year creating his Sinestro Corps.
Yellow Power rings are now fueled by fear instead of willpower, but function the same as their green counterparts. Members of the Sinestro Corps are chosen for their ability to instill great fear in others.
In order to become a member of the Sinestro Corps, one must free themselves from a small prison. With their yellow power ring completely drained of its energy, they must provide it with the spark it needs to accomplish this feat by facing their own greatest fear.
Originally Yellow rings could be charged by Manhunter androids that have yellow power batteries built into themselves, which in turn are connected to the Central Yellow Power Battery on Qward. There are also portable batteries similar to those used by Green Lanterns. Aside from the recharging limitations common among the various Corps, their only known weakness is that their power can be drained by a Blue power ring or disrupted by a Red Power Ring.
According to Ethan Van Sciver, the ring's symbol is based on ancient carvings made by beings who had looked into the gullet of Parallax and survived
