To begin with, there were seven Green Lantern Corps, each representing a colour of the Emotional Electromagnetic Spectrum. The further from the center of the emotional spectrum, the greater the influence a powered light has over its bearer.
Later on three other Corps were discovered, which were White, Black and Ultraviolet.
The Maltusians, the oldest known race in existence of DC Universe, were the first to discover and harness the power of Emotional Spectrum, which is an energy field that is fuelled by the emotions of all sentient beings. Their successors were eventually able to harness the power of emotions of different colours, and create the Lantern Corps DC readers are familiar with today.
All members of the Corps have Power Rings which helps them channel their emotions as different colours of light. This grants the bearers of these rings immense powers like flight, blasting energy beams, creating physical projections of anything they can imagine, and so on. The power of the Lantern Corps are only limited by their emotions which makes them one of the strongest forces in the universe.
But how did each Corps come into being? With all boasting their own complex history, it's time to dive into the stories of how all were created, from Green through to Ultraviolet...
10. Green Lantern Corps
Now, this is one origin story that is well known to every DC fan. The colour green represents the emotion of willpower as well as the centre and most stable Lantern Corps of the electromagnetic spectrum, as green is the central colour of the Emotional Spectrum.
When the Universe was relatively new, the natives of an overpopulated planet called Maltus evolved into immortal beings withholding immense power and intellect. They colonised a planet at the centre of the Universe called Oa and called themselves Oans. Soon after, a renegade named Krona performed a forbidden experiment which nearly annihilated all of creation. In the after aftermath, the Oans made an oath to combat evil throughout the universe as the self-appointed Guardians of the Universe.
After some trial and error, the Guardians decide that their newest forces to combat evil would consist of living beings with free will and strong moral character.
They created the Green Lantern Corps as an inter-galactic police force dedicated to the promotion of order and democracy through out the universe. Each lantern is appointed to protect a sector of the universe and all are armed with Power Rings made by the Guardians, which allowed them to use green light powered by their willpower and imagination to construct objects of any shape and size.
Oath: In brightest day, in blackest night, no evil shall escape my sight! Let those who worship evil's might, beware my power, Green Lantern's light!