Who is Heck Tate and what is his role at the end of the novel?

He is the Sheriff. He protects Boo from publicity by saying that Bob Ewell fell on his own knife.

Heck Tate is the sheriff of Maycomb County. He asks Atticus to defend Tom Robinson, knowing that he will do an honourable job in difficult circumstances. He embodies also the law of natural justice. In deciding that Bob Ewell's death was accidental, he removes the need to pursue the possibilities of Jem or Boo being dragged through a trial as unnecessary as that of Tom Robinson.