What was the name of C.S. Lewis’s fictional planet trilogy’s protagonist?

The protagonist of C.S. Lewis’s fictional planet trilogy is Elwin Ransom.

Elwin Ransom is the central character of Out of the Silent Planet, Perelandra, and That Hideous Strength, collectively known as Lewis’s Space Trilogy or Cosmic Trilogy. Ransom is a philologist and Cambridge academic whose adventures take him from Earth to other worlds and into conflicts involving science, power, morality, and spiritual beings.

The first novel, Out of the Silent Planet, sends Ransom to Mars, called Malacandra in the story. Perelandra takes him to a version of Venus, while That Hideous Strength returns the action largely to Earth and introduces a wider institutional struggle. The three novels share a connected universe but differ strongly in setting and tone.

Mark Studdock is an important character in That Hideous Strength, while Orual belongs to Till We Have Faces and Digory Kirke to the Narnia books. Those names are associated with Lewis, but none is the trilogy’s recurring protagonist.