The Orcs are the primary henchmen of the villains in The Lord of the Rings and The Hobbit, yet not much is known about what they really are. Even J.R.R. Tolkien, the writer who created the world of Middle-earth, has published various, contradicting thoughts on their origins.
These monstrous, humanoid creatures, who are totally devoid of any redeeming qualities, are consistently portrayed as forces of war and destruction. This is what makes them such effective soldiers for the villains of Middle-earth, including Sauron and Saruman. The Orcs could potentially appear in Amazon's Lord of the Rings TV series, since Orcs do exist in the show's setting, the Second Age.
The books themselves don't explain where these creatures from, and while other published works from Tolkien shed some light on their origins, unfortunately there is no perfect answer. Published in 1977, Tolkien's The Silmarillion was a five-part collection of stories that told the history of Middle-Earth, beginning with the First Age. The stories that went into The Silmarillion were being developed by Tolkien as early as 1914. The problem is that Tolkien died before he could finish it, so what fans know of the origin of Orcs comes mostly from other texts of Tolkien's.
What is perhaps the earliest explanation for the Orcs was published in the 1917 book, The Book of Lost Tales, where its stated that they were "bred from the heats and slimes of the earth." However, Tolkien's ideas about the Orcs seem to have evolved since then, since this theory is contradicted by another statement by Tolkien, which says that only Eru Illuvatar (Middle-earth's God) can create life. Also, Orcs apparently reproduce like humans. Tolkien has also suggested that the Orcs were beasts transformed into evil, humanoid creatures.
What seems to be the leading theory is that Orcs were originally humans or Elves who had been corrupted and tortured by dark magic. This was suggested in The Silmarillion, so it's likely the best answer for what created them. It's also the accepted origin for the movie versions as well. In Fellowship of the Ring, Saruman confirms that the Orcs were once Elves. Since this seems to be the story that Tolkien settled on, there's a possibility that it could be explored in more detail in The Lord of the Rings TV series.