Ep 39. Crisis

The Decepticons continue to move the Hydra cannon into range of the Autobot base on Earth, and Optimus Prime and Jetfire mobilise to stop them. Before departing, Prime attempts to give Hot Shot the Matrix of Leadership, but Hot Shot does not feel he is worthy. As the Hydra cannon powers up, Optimus and Jetfire attack the Decepticon ship in their combined form, and disengage as the individual Decepticons strike back. The battle lasts long enough for the cannon to be recharged, and Thrust hits the firing control - but Optimus leaps in front of the blast, and uses the power of the Matrix to nullify it. In the process, however, he sacrifices his own life, and as the Decepticons retreat into space, his body disintegrates into space dust, leaving only the Sparkplug and the Matrix.