"Finn" by Jon Clinch tells the story of Huck Finn's father. It tracks but barely interacts, as he did.
It is really good, but really dark and brutal. So much that it's hard to say I liked it. It's been a while, but I don't think I'd say it was gratuitous, which tends to make me mad.
"Marley" by the same author, but I haven't read it.