Let me tell you a bit of backstory of primordial without spoiling anything.

They all were born in the underworld at the beginning of time. The green and blue met first and started fighting to see who can make the other one serve them. It ended with a tie so the Blue said to Green that they should team up and Green agreed. They both meet Red and Red defeats them both and takes them under him. Then those 3 meet Black and Red and Black fought for a long time and it ended up being a tie.