Overload is a secondary trailer pulled by Optimus Prime in vehicle mode. It is his duty to support the Autobot leader, be omnipresent, seen and felt, but not heard. Overload is a weapons system; in time of need he transforms into two gargantuan shoulder-mounted energy cannons wielded by Optimus Prime. This unique combination makes the Autobot leader more powerful than he has ever been before. Vigilantly standing ready he waits for Optimus' order, "Powerlinx Overload," a signal that his leader needs more firepower - and firepower is what Overload brings.
Bio taken from the 2003 Fleer Transformers Armada Trading Card set.