Which trillogy is based on the novel by John Tolkien?

The trilogy you're likely thinking of is The Lord of the Rings. While it's often referred to as a trilogy, it's technically a single novel divided into three volumes:

* The Fellowship of the Ring

* The Two Towers

* The Return of the King

These three volumes were originally published separately, but are now often collected as a single book.

It's important to note that Tolkien wrote other works as well, such as The Hobbit, which can be considered a prequel to The Lord of the Rings, and The Silmarillion, which is a collection of myths and legends about the creation of Middle-earth.