Master

The Masters are the alien entities who invaded Earth and subjugated humanity with mind control caps in John Christopher's The Tripods series. They are also called the Trions in the television series based off of the novels. They move about Earths' surface in the titular three-legged vehicles and few who have not gone into one of their cities know much about them beyond the Tripods.

Description
The Masters are described in the books as large, heavy creatures with roughly triangular bodies. They have three legs which are short but still allow them to move surprisingly fast. They have no arms but possess three tentacles and have three eyes above a combined nose/mouth structure. They have green skin, sometimes with patches of brown.

In the television series, their appearance is slightly different. They walk on three legs, with a thick central limb serving as the torso. The two outer limbs are slightly thinner and descend from a round head and shoulder area at the top.

Biology and Psychology
The Masters are known to be from a planet with a high gravity and very different atmosphere to Earth's. The air they breathe is greenish in color and fatal to humans, although it can be breathed with the help of a mask which filters out the poisonous part.

They are known to suffer from an illness called simply The Sickness, which causes feelings of illness, fever and weakness, and those with more brown in their skins are more prone to it. They are also left paralyzed and incapacitated if they ingest alcohol.

The Masters view their human servants in a manner much like pets, showing affection, petting them, etc. However, they all have different personalities and ways of dealing with their servants. Will, the books' protagonist, finds his relatively kind, while another boy,Fitz, is often beaten by his master for entertainment.

They are attracted to beauty and preserve many things from the worlds they conquer, including many of the human girls brought into their cities. They also have an affinity for the color green, which is in their skin and their air, and for the number three, which is in their anatomy and their vehicles.

History
The Masters came to Earth in the mid 1980s. Initially, they landed three of their Tripod vehicles on Earth: One in Great Britain, one in Russia and one in the United States. The Americans just waited and watched, and the Soviets destroyed theirs instantly. The British tried a friendly approach with classical music, but when the Tripod destroyed a house and kidnapped one of the humans inside, they sent tanks and planes to destroy it.

People initially laughed about the Tripod invasion, believing that the aliens had been easily destroyed. But the Masters had realized that they could not win against humans in open combat, and turned to another method. They utilized television technology to create a program called The Trippy Show, which hypnotized many of those who watched it.

At first, the 'Trippies' were a nuisance more than anything, but over a couple of weeks, their numbers grew and they began causing problems in cities and leaving home to join communes. More Tripods landed, and the Masters gave their followers mind control caps made of metal and rubber. They were first given to those who were willing, and then put on others by force.

For a time, civil war raged, with the Capped and free fighting for supremacy. However, as more and more people were capped, there were fewer free people to fight. Eventually, the removable caps were replaced with wire caps embedded into each human's skull. The resistance dwindled to a few small pockets, and though free humans survived for several months in submarines, even they were eventually hunted down.

After a hundred years had passed, few even remembered where the Tripods came from. Large cities were abandoned and humans returned to a medieval-like agricultural life. The Masters ruled from three domed cities they built. Every human was Capped at age 14 and contests were held to choose the strongest boys to serve the Masters in their cities. A constant supply of new slaves was needed because the harsh conditions of the cities quickly wore out the humans who were brought there.

Defeat
The Masters were defeated after a resistance group sent spies into the cities and learned that the Masters' ultimate goal was to transform Earth into a place they could live, killing all Earth life in the process. After a Master named Ruki was captured, it was discovered that the Masters could be overpowered and paralyzed by putting alcohol into the water supply. Three teams set off, and two of the attacks succeeded. Once the cities were powered down, the caps of those inside no longer worked, and the humans could be helped to escape.

The third attack failed, and an alternate plan had to be formulated. A bombing raid was carried out. Primitive airplanes were first used, but the Masters saw the attack coming and used an electromagnetic pulse to shut down the engines and crash the planes. A second attempt was made soon after with hot-air balloons, and it too appeared to be failing, as the bombs bounced off and detonated too high to damage the city's dome. However, one of the protagonists plants his bomb, sacrificing himself but accomplishing the goal of destroying the city.

As humans began to rebuild their civilization, the alien mothership approached Earth. It was feared that they might bomb Earth, but they struck only their three destroyed cities, obliterating them and the humans studying the technology inside to prevent reverse engineering of their technology.