Mavericks are evil Robots that were desended from the Kuiper Droids who had the 20,000 year old war with Ra-Moon. the Mavericks were re-created by Sigma who plans to wake Ra-Moon from eternal Slumber and corrupting Dr. Willy to attack Megacity.
10,000 years after the Maverick Wars. the Kuiper Droids escaped to Earth and hid underground. Then Ra-Moon created his first Mavrick out of a Kuiper Droid (Who will be later Sigma). Sigma survied many years and he corrupted Dr. Willy and made him attack Mega City and brainwashed The Robot Masters as Mavericks. More were created by Ra-Moon, Dr. Willy and Sigma.