Test pilot Hal Jordan was chosen to become a member of the Green Lantern Corps. His fearless and heroic nature have proven him worthy of the Green Lantern ring many times over, and is considered one of their greatest heroes.
The Sinestro Corps are the enemy of the Green Lantern Corps. Led by the disgraced Green Lantern Sinestro, the Corps uses the yellow energy of fear much like their rivals Green Lantern. Hal Jordan has used these yellow rings in combat against the Sinestro Corps and their allies.