The Creators are a group of agents who were the initial members of the organization WICKED (World In Catastrophe Killzone Experiment Department). They created the Trials in order to stimulate certain patterns in the Killzones of two groups of subjects. They would then use these patterns to work out what it was that made their brains immune to the Flare, and use this knowledge to create a cure. Thomas, Teresa, Rachel, and Aris worked alongside them.
However, The Creators weren't immune to the Flare, and so when there was an outbreak in WICKED, Thomas and Teresa had to kill them all, being the only ones immune. This event was known as The Purge. After this, Thomas and Teresa had to train the founders' successors, including Janson.