Who is Huckleberry Finn in Tom Sawyer?

Can you please explain who Huckleberry Finn is in relation to Tom Sawyer? I understand that both characters are from Mark Twain's classic novel, but I'm curious about the dynamics between them. How does Huckleberry Finn's character contribute to the story and what role does he play in Tom Sawyer's life? Is he a friend, a sidekick, or something else entirely? I'm eager to learn more about this intriguing character and his relationship with Tom Sawyer.