Sinestro wields an other-dimensional ring, from which all his powers derive. All power ranks are based on the user's will power (equal to his Psyche rank, which is Monstrous for Sinestro). The ring must be recharged periodically from a Green Lantern's power-ring beam, or it will cease to operate. The ring has the following capabilities:
Spatial & Dimensional Navigation * Civic Administration * Negotiation
The Legion of Doom * The Secret Society of Super-Villains * The Weaponers of Qward.
When he was chosen by the Guardians of the Universe on Oa to become a member of the Green Lantern Corps, Sinestro of Korugar was judged to be a being of honor and fearlessness. Over the ages they had chosen tens of thousands of beings to wear the emerald power ring of the Green Lanterns and had never misjudged one. Until Sinestro.
At first Sinestro proved a capable and conscientious member of the Corps, faithfully patrolling and protecting his assigned Sector 1417, but soon he began to see the potential in being the wielder of the power ring. He set himself up as absolute arbiter of all disputes on Korugar, dispensing his own increasingly warped sense of justice and declaring himself dictator.
At that point the Guardians intervened and brought Sinestro to Oa for judgment. Finding Sinestro guilty of violating every tenet of the Corps, the Guardians stripped him of his power ring and rank and banished him to the planet Qward in the Anti-Matter Universe to learn first-hand the fate of those inhabitants of a world where true evil rules.
That was not the lesson Sinestro learned from Qward's natives, the Weaponers. They were a race who lived only to create weapons of conquest and see them in use on helpless others. Sinestro saw this as a power base to use as his launching platform for universal conquest.
Sinestro returned to his home universe shortly after and had his first encounter with Hal Jordon, the Green Lantern of Earth. Sinestro and Green Lantern would clash repeatedly over the years, until his defeats at the hands of this courageous Corps member became a deadly obsession with him. Armed with a power ring (created for him by the Weaponers) that emitted a yellow power beam (due to a necessary impurity in the power battery that charges the Corps' rings they are powerless against anything yellow in color), Sinestro waged an endless war with the Green Lantern and his comrades in the Corps.