Natromo was a male sapient being that was native to the planet Nok. Centuries ago, his world came under attack from alien invaders that attempted to enslave the populace who were to be shipped away from their planet. During this time, the people of Nok discovered a wellspring within a cavern that tapped into the Indigo Light of Compassion within the Emotional Spectrum. They coated their weapons with the light which led to their enemies temporarily feeling remorse for their actions. At this time, Abin Sur of the Green Lantern Corps arrived on Nok where he helped defeat the invaders. Afterwards, the people of Nok returned to the Forbidden Jungles whilst Natromo worked alongside Abin Sur. Together, they went into the caverns where the Indigo Light was shown and Sur revealed the future dangers