The GRE (Global Relief Effort) is the main antagonistic group that appears in the 2015 Zombie game Dying Light.
After the outbreak in Harran, with ties to the Ministry of Defense. The force, size and power of the Global Relief Effort is not detailed in Dying Light but subtle details are dropped throughout the game. The Global Relief Effort is the group responsible for flying cargo planes over the quarantine zone and sending air drops of food, medical supplies, flares and Antizin into the city. After Kadir 'Rais' Suleiman went rogue as repentance for the GRE's failure to evacuate his crippled brother, the GRE sent their agent, Kyle Crane into the quarantine zone to locate and identify Rais and the file he'd stolen from the GRE.
The GRE periodically sends humanitarian aid to the quarantine zone via a C-130 Hercules cargo plane. Besides this, the GRE is also responsible for manufacturing and delivering Antizin, and keeping the Ministry of Defense from firebombing Harran. However, most of their abilities are shown subtly throughout the course of the game. The GRE was tasked with maintaining order in Harran after the outbreak, but failed to do so as Rais went rogue after the death of his brother, Hassan. Rais threatened to publish a highly-sensitive file that represented a huge threat to mankind, as it contained a full structure of the Harran virus. To counter this, the GRE instituted a city-wide communication jam to ensure that the file would never be published.
Harran operations during 2014
Somewhere in the year of 2014, freelance GRE operative Kyle Crane is inserted in the city of Harran via a C-130 tactical jump. After landing, he is attacked by Tahir and two other bandits. He quickly dispatches them with his firearm, but is injured in the process and bitten by an infected, drawn by the gunshots. After being rescued by two runners (Jade Aldemir and Amir Ghoreyshi), the trio attempt to escape the mob of infected, but Amir sacrifices himself to save Kyle and Jade.
Throughout the entire course of the game, Crane maintains an undercover identity and becomes a runner of the Tower. He is tasked with retrieving a highly-sensitive GRE file, code-named "Tempest", that contains a complete virion structure of the Harran infliction. However, the GRE discover Zere's research, and they oblige Crane to secure it. Later in the game, it is revealed that the GRE is not working on a cure, but instead they plan on weaponizing the virus and selling it to the highest bidder. At the sound of this news, Kyle deconspires himself to his fellow colleagues, and attempts to confront Rais, who's plans were to sell Zere's information on the virus to the Global Relief Effort. Rais transmits the information and claims that the GRE had planned to weaponize the virus, not cure it.
However, the Ministry of Defence had become impatient with GRE's lackluster attitude to solve the outbreak and forcibly took over GRE HQ. GRE also found itself stripped of all authorities regarding Harran Containment. But in DLC Dying Light: The Following, The Ministry of Defence once again handed over authority of Harran Outbreak to GRE.
Besides the C-130 Hercules airplanes that constantly drop Antizin for survivors, the GRE never actually appears physically. Only two known representatives of the GRE are heard and unseen, a female voice that communicates throughout the game with Kyle via his GRE-issued radio, giving him instructions and indications; and the pilot at the beginning of the game.