Radiak was a warrior and a famous hero among the Av-Matoran. Turned into a shadow Matoran by Vamprah, he proved to be just as fierce a fighter for evil as he had been for good. When Antroz and Radiak were physically linked, both gained new abilities. Antroz was able to see through Radiak's eyes via a mental link. Radiak was able to slow opponents, making them feel too lazy to act. Radiak was turned back into an Av-Matoran thanks to the efforts of Takanuva. At the end of story year 2008, he lived on Metru Nui.
Radiak flew with Antroz, using his special power to slow the actions of the Toa and make them easy targets.