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Many people are now discovering the stories of JRR Tolkien for the first time, and have questions which can't be answered simply by reading the books. For example, who is the Necromancer in The Hobbit? And what the devil is a Balrog? What does Shelob have to do with anything? This information is all found in Tolkien's book, The Silmarillion. For those who do not have the time or the patience to look them up, here are some answers.
The Villains Before...
Before The Lord Of The Rings, and even before The Hobbit, there were several evils that impacted upon Tolkien's world, setting up the complex interweaving of stories that we know today.
Morgoth ('dark enemy of the world'), also called Melko or Melkor ('He who arises in might') was the original evil of Tolkien's world, a proverbial Lucifer. Originally one of the Ainur (the gods of Middle Earth), Morgoth was great and knowledgeable in many things, and possessed all the gifts and skills the other Ainur possessed. Morgoth sought to become more powerful than the Illuvatar (the 'All Father' - the greatest god), and started a holy war of sorts for control of Middle Earth.
The children of the Illuvatar, elves and men, were fair; but the children of Morgoth were foul and wicked. They were orcs and fire demons called, among other things, Balrogs ('demons of might'). Morgoth was the creator of the orcs, and made them by capturing some elves and warping and twisting them until they were no longer the pure creatures they used to be. He cared nothing for anything or anyone except himself. In time, he became a shameless liar, and fought with elegant words as well as with his evil armies.
Don't get the impression that he was some sort of evil-looking monster. He could take any form he chose, and was often seen in a noble and beautiful form, to easily sway the weak-minded. Yet he didn't always win. He was beaten several times, and chained up. In the end, after one final battle, he was cast out of the world into the Void for all eternity. He left someone behind, though - the lieutenant we know as Sauron.
Ungoliant was a foul spirit who took the shape of a great spider. Ungoliant fed off light, or rather, hated it. Her great webs caught it and sucked it in, and the more light she fed upon, the greater she grew.
Morgoth made a pact with her to help with the downfall of the Valar and the Eldar (the first elves). The Valar had two great trees, the Trees of Valinor ('Telperion' and 'Niaquelote'), and they shone with a holy light. They were a blessing to all, and a sign of hope. Of course, Morgoth didn't much like them in the hands of any but himself, if he even liked them at all, and he helped Ungoliant kill them, and steal their light.
Later, Morgoth refused his end of a bargain he had made with Ungoliant, and she attacked him. She was so strong after taking the light of the Trees that she could have killed him, and would have done so had it not been for his cries for help, which were heard and heeded by the Balrogs. It was said that the cries were so hideous that they could still be heard ever afterwards.
Ungoliant fled, and had offspring of a similar nature to herself. The last of these was Shelob, who took up residence in the mountainous borders of Mordor.
The Evils in 'The Hobbit'
The full explanation of Gollum is found in The Fellowship of the Ring, but here is a brief overview.
Gollum started out as a small Hobbit-like creature named Smeagol. He and a friend named Deagol were fishing on the banks of the Anduin river1 when his friend saw a glint of gold. He dived in and came up with a gold ring in his hand. Smeagol wanted the ring. It was his birthday, so by Smeagol's reasoning the ring should be his, though this was mostly due to the fact that the ring in question was the One Ring (see below under The Lord of the Rings). Suffice it to say that the ring had an immense attraction for living beings, and Smeagol killed his friend to get it. He went home and discovered that it could render him invisible.
He took up thievery but was shunned by his people. He wandered to the Misty Mountains, and hid under them in a dreary underground lake. All this while the ring corrupted him, making him the vain creature he is in the books.
Where Be There Dragons?
Dragons were not common in The Hobbit, as can be seen. Smaug seemed to be one of only a few.
Dragons in Middle Earth were the creation of Morgoth, and their father was Glaurung, a firedrake2 of the north (hence Smaug came from the north). They were bred in Angband (the iron fortress of Morgoth, literally meaning Iron Prison or Iron Hell), and became very numerous and powerful.
They lived long lives and therefore were often very wise, but they had a few weak points. The first of these was that when young they were easy to kill, just like shooting the proverbial sitting duck. Their armour was weak, and so were their minds. Secondly, they exhibited enormous greed, and this made them rather hard to control. Their third weakness was a result of their second, since when a dragon found itself large amounts of wealth it would guard it, rarely leaving, and tend to take century-long naps.
The last dragons simply vanished from all records. Their whereabouts are unknown.
See under Sauron, below.
'The Lord Of The Rings' - The Evil Therein
Bum Bum Buuummm... Sauron
Sauron was originally a lieutenant under Morgoth, and it was said that he would have been just as evil as Morgoth even if he was not serving him. Sauron's personality and ethics can best be described by a long string of expletives - let's just say he did the most downright cruel things of anyone who ever existed in Middle Earth.
Also known as Gorthaur the Cruel, Sauron started out as a Maia, one of the spirits of Middle Earth. He was the commander of Angband, and was as sadistic as they come. He was also somehow incredibly clever, and just as good a public speaker as his master. When Morgoth was banished, Sauron ran off rather than suffer the wrath of his opponents. In time, he gathered strength, and carried on where Morgoth had left off, being a general pain.
In the tale of Beren and Luthien (quite a good read, actually), he is described as capturing a man's wife and letting him see her being dragged away in torment. Then he captured the man, bargaining with the man's wife for information and promising that they would leave together. Once he had got the information he revealed that what the man saw was just an illusion (surprise, surprise!); his wife was dead. And yes, he would indeed be joining her.
After the fall of Morgoth, Sauron became well versed in wizardry, and took a leaf out of his master's book. He took on a fair appearance and got on everyone's side. During this time, with the help of the elves, they forged the Great Rings, the Rings Of Power. Then he backstabbed his way to the top. In secret, he forged the One Ring, a ring that had control over all the other rings and whoever used them. However, this ring was lost after several battles; but for that, he would have controlled the world. What happens after this point is revealed in The Lord Of The Rings, and for more information on all his cruel exploits, one simply needs to look there.
Very little is known about either Saruman or his brethren, the wizards. All that is known is that there were five of them, they came across the sea, and were originally from a spirit called Istari.
There was one white wizard (Saruman), one grey (Gandalf), one brown (Radagast), and two blue wizards, whose names are never mentioned and who apparently never did anything of value. Saruman was their leader, and was wise, though it was suspected by many that Gandalf was wiser, and was simply pretending otherwise.
The wizards came to fight Sauron, and were fit for the job. Unfortunately Saruman started getting greedy and soon allied with Sauron. But fearing complete destruction he hoped maybe to destroy Sauron first and rule in his place.