What is the origin of the wargs, and are they featured in any of Tolkien's works other than LOTR and the Hobbit?

Question

In The Lord of the Rings, wargs are commonly ridden by orcs and are also featured in the Hobbit films (although these are not considered canon.) Is the origin of the wargs known and are they featured in any of Tolkien's works which take place before The Hobbit?

Answer 1

The origin of the wargs is unknown.

From Tolkien Gateway, sourced to Tolkien's Letters (Letter 297 and a letter to Gene Wolfe) and the book The History of the Hobbit, Part One: Mr Baggins, edited by John Rateliff:

Wargs were an evil breed of demonic wolves, suggesting that they were inhabited by evil spirits. The origin of the breed is unknown - perhaps they were among the creatures bred by Morgoth in the Elder Days. In any case, Gandalf listed the Wargs among Sauron's servants in the late Third Age.

They feature quite prominently in The Hobbit, being one of the five armies in the eponymous battle. They also appear in a single scene in The Fellowship of the Ring, and aside from that they do not seem to appear in any of Tolkien's works, beyond the occasional mention in his Letters or in linguistic discussion of the words and names of Middle-Earth.

What about the werewolves?

Werewolves were servants of Morgoth created by Sauron in the First Age, and there are fan theories that the wargs of the Third Age were descended or bred from these. But there seems to be little evidence for this in canon (you can read some speculation about it here), and the two are certainly distinct enough to be listed by Gandalf as separate beasts:

Not all [Sauron's] servants and chattels are wraiths! There are orcs and trolls, there are wargs and werewolves; and there have been and still are many Men, warriors and kings, that walk alive under the Sun, and are yet under his sway.

_{-- Gandalf, The Fellowship of the Ring, Book 2, Chapter 1: Many Meetings}