Who were the first great nonwhite characters in English literature? Well, if we include plays, we might say the first was Shakespeare's Othello. Along with perhaps Cleopatra and the pseudo-Indian Caliban.
If we limited ourselves to novels, we could add Oroonoko in Oroonoko (1688), arguably the first English novel. But few people know about this royal African slave. Then there was Friday in Robinson Crusoe (1719), another contender for the first English novel.
Two nonwhite characters in early American novels were James Fenimore Cooper's Chingachgook and Uncas in The Last of the Mohicans. Herman Melville was one of the first novelists to write about indigenous or "exotic" characters: Queequeg in Moby-Dick, Typee, Omoo. Mark Twain wrote about Injun Joe in Tom Sawyer, Jim in Huckleberry Finn, and Pudd'nhead Wilson. Helen Hunt Jackson wrote her romantic novel Ramona.
Outside of novels there was Metamora in the 1829 play of the same name and Hiawatha in the 1855 epic poem. No doubt there were plays about Pocahontas and Minnehaha too. Along with minstrel shows featuring white characters in blackface and Wild West shows featuring savage Indians.
Around the time of the Civil War, people began writing seriously about black characters. Until then, most of the nonwhite characters in English literature were Indians and other indigenous people. Someone could write a thesis on this, but I suspect Native characters played a notable role in the development of English and American literature.
For more on the subject, see The Best Indian Books.
Below: Edwin Forrest as Metamora in 1829.