Who was Tom Sawyer's best friend in Mark Twain's novels?

The Adventures of Tom Sawyer is an 1876 novel by Mark Twain about a boy growing up along the Mississippi River. It is set in the 1840s in the town of St. Petersburg, which is based in Hannibal, Missouri, where Twain lived as a boy. In the novel, Tom Sawyer has several adventures, often with his friend Huckleberry Finn. Originally a commercial failure, the book ended up being the best-selling of Twain's works during his lifetime.

Source: Wikipedia