A related question is whether his immunity to the Ring means he is more powerful than Gandalf.  I suggest not, because Gandalf indicates at the Council of Elrond that Tom is not particularly powerful, and because power tends to make people more vulnerable to the Ring, not less.  Instead, I believe that Tom is immune to the Ring because he has no desires for the future, but lives each day as it comes.

The orcs were warped versions of creatures created by Eru, i.e. God.  Melkor, or Morgoth, i.e. Satan, warped them.  What they started out as was unclear, even to Tolkien.  But it is clear that Morgoth could not create life, and therefore had to work his evil on captive creatures of some kind.

The Uruk-Hai were bred by reducing men to the level of orcs so that they would mate with orcs.  Sauron did this about 500 years before the War of the Ring, and Saruman did it again shortly before the War of the Ring.

The goblin orcs of Moria were the more ordinary breed of orcs, bred from creatures of Eru by Morgoth, as noted above.

As Alveric reminded me, one elf, Legolas, came to Helm's Deep in the book.

The Valar, probably with the help of Eru, created the Istari by placing Maiar spirits in the bodies of Men.  The Valar and Maiar are roughly equivalent to greater and lesser angels.  There is more about the Istari in Unfinished Tales, and more about the Valar and Maiar in The Silmarillion.

The Thain (Pippin's dad, and later Pippin) is technically the King's representative among the hobbits, and the Mayor is the elected leader of the Shire, while the Master of Buckland (Merry's dad and later Merry) is the leader of Buckland, but all of those positions are largely ceremonial.  For the most part the hobbits seem to live just fine without a ruler, in a sort of benevolent anarchy.

“I dislike Allegory - the conscious and intentional allegory - yet any attempt to explain the purport of myth or fairytale must use allegorical language.  (And, of course, the more 'life' a story has the more readily will it be susceptible of allegorical interpretations: while the better a deliberate allegory is made the more nearly will it be acceptable just as a story.)” (From Tolkien Letter # 131.)