The Return of Optimus Prime, introducing the title characters to the Transformers universe in a different way. Whereas in western fiction, the Headmasters result from the merging of a Transformer with an organic alien being from the planet Nebulos, the Headmasters of the Japanese series are a group of small Cybertronians who departed the planet millions of years ago and crash landed on the inhospitable planet Master. To survive its harsh climate, a select few of the most-highly trained constructed larger bodies called "Transtectors," to which they connected as heads. When a group of rebellious Headmasters led by Zarak joined with Galvatron's Decepticons in an attack on Cybertron, the Autobot Headmasters, led by Fortress returned to their home planet to aid in its defense. The situation soon went from bad to worse when it was revealed that Vector Sigma, the mega-computer at the planet's heart, was destabilizing, and Optimus Prime again sacrificed his life to save Cybertron. This soon proved to be only delaying the inevitable, however, when a bomb attack instigated by Zarak turned Cybertron into a burnt-out, inhospitable husk. Rodimus Prime departed to search for a new planet for the Transformers to live on, leaving Fortress in command, operating from the planet Athenia. Meanwhile, Zarak replaced Galvatron - who had vanished in the explosion - as Decepticon leader, constructing a personal Transtector so that he could battle Fortress's own giant form, Fortress Maximus, and redubbing himself Scorponok. Although populated mainly with new characters, The Headmasters did continue to feature characters from all previous seasons, including new versions of Soundwave and Blaster, rebuilt after a duel that destroyed them both as Soundblaster and Twincast. Human Daniel Witwicky and his young Autobot friend Wheelie also played major roles in the series, serving as the youthful characters for the audience to identify with. More new characters continued to pour in when Galvatron returned to leadership and the Decepticons embarked on a space voyage, ransacking planets in a chain of stories that introduced the Horrorcons and Autobot and Decepticon Clones. The return to Earth was no less momentous, as the Decepticon ninja six-changer Sixshot killed Ultra Magnus, and the Autobot Headmasters finished off Galvatron. When the Decepticons then returned to Master, refugees from the planet were caught in a plasma bomb accident that fused them to the arms of several Autobots and Decepticons, creating the Targetmasters, and in a final move, Scorponok