Background (see https://greenlantern.fandom.com/wiki/Emotional_Spectrum#Yellow.2FFear):

Yellow is a color close to the center, and represents the emotion of fear. A being capable of instilling great fear in others is capable of wielding this power. The yellow light was finally harnessed by Sinestro of Korugar and the Anti-Monitor of Qward to form the Sinestro Corps, an organization that would bring order to the universe by instilling those who would defy authority with fear.