Alright, let me break down the main crew in 'Project Hail Mary'. The absolute heart of it is Ryland Grace, a middle-school science teacher turned amnesiac astronaut. We meet him as he wakes up alone on a spaceship with no memory, and the book is essentially him piecing together who he is and why he's there. His role is the everyman genius—his background as a teacher makes him great at explaining the wild science he's doing, which is the whole fun of the book.
Then you've got Rocky, who isn't human. He's an engineer from the planet Erid, and he's described as a spider-like creature made of rock. His introduction is a masterpiece of first-contact writing. Rocky's role is the ultimate partner—loyal, brilliant, and emotionally steadfast. Their friendship, built on shared desperation and a language of musical notes, carries the entire emotional weight. The other key human is Eva Stratt, the ruthless, pragmatic director of the Hail Mary project on Earth. She's the one who essentially conscripts Grace, and her 'by any means necessary' attitude drives the bleak, high-stakes setup back home.