A Powermaster is one of several Transformers who have been binary bonded to a partner who serves as their external power supply. (See also Headmaster, Targetmaster)
History
Powermasters were a creation born out of necessity. After years of war on their planet, the Nebulans no longer cared whether the Autobots or Decepticons won, as long as the fighting stopped. When the Headmasters and Targetmasters left their planet to seek reinforcements from Earth, the Nebulans took advantage of the opportunity to poison all of their fuel and energy sources, tainting it in order to render it unusable by any Transformer (a tactic that had also been used to great effect by Sparkplug Witwicky, on Earth).
The scientists who had devised the toxin, a pair of Nebulans named Hi-Q and Hi-Test, however, had a falling out soon after their success. Hi-Test felt that they deserved wealth and power as their reward for saving the planet, while Hi-Q argued that they had only done what was necessary. When a pair of Decepticons named Darkwing and Dreadwind appeared to menace the planet, and were immobilised by the tainted fuel, Hi-Test saw an opportunity to act. Undergoing a binary bonding process with the inert Decepticons, Hi-Test changed himself and his ally Throttle into the first Powermasters.
Using this new process, the Decepticons were able to function on the posioned planet of Nebulos by using their Powermaster partners as living batteries. When the Autobots arrived to stop their reign of terror, they succumbed to the poisoned fuel sources and were helpless to combat the Decepticons until Hi-Q took action and used the same binary bonding process as his rival Hi-Test, bonding himself to the body of Optimus Prime. His fellow scientists, with one exception, followed suit in bonding themselves to fallen Autobots as well. Most of the Transformers known as "Powermasters" were the result of this initial bonding - the procedure is otherwise quite rare.
Terminology
The term "Powermaster" refers specifically to a Transformer who had been bonded to another creature which he uses as a power source. This is not, however, to be confused with a similar term, "Godmaster". The largest difference between a Powermaster and a Godmaster is the source of their transformation ability and their choice of partners. While a Powermaster transforms and functions due to their special armour and cybernetic implants, a Godmaster's ability comes from their Master Braces, special bracelets which allow them to channel the power of Jinchokon energy into their partners. Also, a Powermaster is paired with a sentient, living Transformer, while a Godmaster is partnered with a non-sentient, but still "living" Transtector. The Godmaster controls the Transtector, but the Powermaster does not directly control the Transformer.
Technology
As with most forms of Nebulan "Master" technology, the key to the Powermaster procedure lies in the extensive cybernetic surgery and specially designed power armour used by the subject. These changes allow a Nebulan (and presumably would also allow a human, although there are no known human Powermasters) to transform into a powerful engine/power cell and bond themselves to a properly modified Transformer. The primary advantage to this procedure is survival: Powermaster partners are able to filter and counteract the radioactive toxins within Nebulan fuel, allowing a Transformer who has been posioned to function normally. Without this bonding, a poisoned Transformer will be unable to move or transform on their own as the poisions ravage their system.
Aside from serving as an advanced filtration system for any impurities or toxins that may be in their associate's body, a Powermaster partner can also function as a power booster or turbo accelarator, giving the Transformer he is bonded to a surge of additional power for increased strength or speed in dangerous situations. This benefit allows a Powermaster to be much faster or stronger than most normal Transformers for brief periods of time. In addition, a Powermaster engine is more adaptable and efficient than a standard Transformer fuel cell: far from requiring energon or refined fuels, Powermasters can run on almost any energy source - including food. This makes it much easier for a Powermaster to adapt to the available resources, without needing to waste time or energy converting them into a more palatable form.
Flaws
Being a living battery places a heavy strain on the bodies of those who wish to be Powermaster partners. The procedure often leaves the people involved with extremely high metabolisms, meaning that they need to eat large quantities of food at regular intervals just to keep themselves from starving to death. The Transformer that they are paired with is often drawing his power directly from their own life energy - if stretched too far they can easily be left exhausted, hungry, or even dead. Over time, the bonding procedure for Powermasters seems to be similar to that of some Headmasters, in that there is a risk of both partners being absorbed into a single being with only one mind and identity (this happened to Hi-Q, who over time began to change and merge with his Transformer counterpart until he actually became Optimus Prime).
A Transformer who has undergone Powermaster formatting is also at something of a disadvantage if seperated from their partner. Even more than a Headmaster, a Powermaster needs his bonded partner to function. Without them, he cannot transform, fight, or even move. His partner is basically an advanced form of life-support, and should they be lost, killed, or even damaged, the Transformer will be in mortal danger.