Ryland Grace is the main character in the science fiction novel "Project Hail Mary," written by Andy Weir. He is an astronaut and a biologist who wakes up alone on a spaceship, tasked with saving Earth from an extinction-level threat caused by a microorganism. As the story unfolds, Ryland discovers he has amnesia and must piece together his mission. He encounters an alien named Rocky, forming an unlikely partnership to solve the crisis. The novel explores themes of survival, friendship, and the power of science in overcoming challenges.