The Soul King is a genetic experiment gone wrong. He was created accidentally by the Kiladako.
The Soul King is a shapeshifter without any single form. He can speak, but often does not have anything intelligent to say. He has an obsession with always looking beautiful.
The Soul King is very powerful, and can manipulate matter and energy at will.
Origin
The last thing the Kiladako needed to research about tokis was the weird elemental magic that the Tekels were capable of.
They had a test subject, Kyari-Tekel, to run experiments on. The mission to discover the source of magic ran over-budget with confusing test results.
In the process of figuring this out, the Kiladako created a horrible magical experiment which escaped. In the end, the project was eventually abandoned.
The Soul King continues to run rampant through galactic space, terrorizing as many individuals as he can.