Nitro
Nitro (previously dubbed Birdmen) are humanoid creatures with a bird-like face that possess incredible physical abilities and high intelligence. The "New Model" GT Robo is based off of this creature. According to Chief Mansam the Nitro know how to obtain "GOD", and it is said that Acacia discovered GOD by observing the Nitro. Acacia gave the task of isolating and observing the Nitro to his best pupil, Ichiryū.