Gahdok is one of the two Bahrag, who was created by the Great Beings along with Cahdok to be the rulers of the Bohrok Swarms. Their mission was to clean the island of Mata Nui whenever the Great Spirit Mata Nui was to awaken.
After Teridax's first defeat by the Toa Mata, he was extremely weakened. In an attempt to buy time while he recuperated, Teridax awoke Gahdok and Cahdok because he knew that they would unleash the Bohrok Swarms. Unaware that it was not the right time, Gahdok awoke the Bohrok to clean the island of Mata Nui, starting the whole Bohrok Swarms saga. After the Toa Mata had gathered one of each Krana from every Bohrok, they were able to gain access to the lair of the Bahrag. When the Toa Mata entered the Bohrok Nest, Gahdok and Cahdok fought against them. In the end, the Toa Mata combined their powers to seal the Bahrag inside a cage, which severed the Bahrag's connection to the Krana and deactivated them. This action also caused the Toa Mata to fall into tubes of Energized Protodermis and be transformed into the Toa Nuva.
The defeat of the Bahrag also caused the awakening of the Bohrok-Kal, six special Bohrok created by the Bahrag in case they were defeated. The Bohrok-Kal eventually found where Gahdok and Cahdok were being held and defeated the Exo-Toa who guarded them. Before the Bohrok-Kal could free the Bahrag using the Toa Nuva's Toa Symbols, which were the keys to the Bahrag's prison, the Toa Nuva defeated the Bohrok-Kal before the Bahrag were freed.
In addition to the abilities listed in the Powers & Battle Rankings chart to the right, the Bahrag are also symbiotic, which means that Gahdok draws power from her sister, Cahdok. When together, the powers of the Bahrag become stronger and a powerful barrier forms around them. Since both Cahdok has all the powers of the Bohrok Swarms, that means she has the Lehvak's power of acid.