Whose name appears on just about every page of this book? Kim's. When you close your copy of the novel and look at the front cover, what do you see as the title? Kim. These are both pretty good clues that Kim is the main character. The novel Kim tells us the story of young Kim's development from a lying, cheating, fun-loving kid on the streets of Lahore to a serious, dedicated, responsible member of the British Indian Secret Service. Since it's his story that really structures the whole plot of the novel, it would be tough not to call Kim our protagonist.
While the lama may not appear in every chapter the way our main main character Kim does, we still think that we can call him the book's second protagonist. After all, the lama's quest for the River of the Arrow begins even before Kim really knows what he's looking for in life (beyond this vague and exciting prophecy about a Red Bull in a green field, of course). And the lama's Enlightenment is also what ends the novel, as we discuss in our section "What's Up With the Ending?"
Not only does the sympathy between the lama and Kim give Kim a reason to leave Lahore in the first place, but the lama also undergoes his own journey of self-discovery over the course of the book. The lama is the only other character besides Kim who actually changes in this novel, so we feel pretty confident in giving him main character status.