WCKD

World In Catastrophe  Killzone Experiment Department, generally abbreviated to WICKED (WCKD in the movie adaptation), is an organization originally formed to find a cure for The Flare. After the Sun Flares, the remaining governments of the world combined their resources to set this organization up, for the world was in desperate need for a cure. For the purpose of experimenting, they selected about a hundred teenagers, including Immunes and Control subjects. They passed them through The Trials, such as the Maze and the Scorch, which involved various variables which were designed to stimulate the Killzone of the brain so they could record specific patterns. They planned to use these killzone patterns to discover why these subjects' brains were able to fight off the Flare, hopefully allowing them to produce a cure. Thomas, Teresa, Aris, and Rachel are all WICKED members that went through the trials.
Throughout the series, Teresa Agnes and Ava Paige frequently mention that WICKED is good, because saving the human race is worth the sacrifice of a few members of it. However, WICKED eventually strays from this goal when they fail to obtain a cure for the Flare, and embark on dangerous activities (depleting the Immunes) to keep their organization alive. Thus, Teresa turns against WICKED, and Ava Paige is among the few remaining members of WICKED who oppose the idea of repeating the trials (which would sabotage the last remaining hope for the human race).
WICKED's ultimate fate is unknown, although it is safe to assume that WICKED is destroyed by The Right Arm during their attack in The Death Cure.