That person calls himself "Mud" and is played by Matthew McConaughey. Some are calling this the actor's finest role which may be true (putting aside his work in films such as Frailty and Lone Star). He is also surrounded by other fine actors--especially Tye Sheridan as Ellis, the young protagonist. Sheridan brings a complex young man to life--he is coming of age with girls, he is dealing with the break up of his parent's marriage and then he discover Mud. He truly shines in the role.
His best friend, Neckbone, played by Jacob Lofland is also stellar. Both seem true in their roles. You never get a whiff of "acting" in their acting. They bring these kids to life and, if anything, steal a great deal of McConaughey's thunder.
Add to these two Ray McKinnon, Michael Shannon, Sam Shepard and Reese Witherspoon and you have quite an ensemble cast. Their screen time is never wasted. They make the most of every second.
Until you think on it a little more.
We love happy endings. We accept sad endings. Sometimes were are disturbed when things end somewhere in between. Yet that is how life is most of the time. The best doesn't always happen but neither does the worst. Love may not always triumph but that doesn't mean it is utterly worthless.
Characters, major and minor, make decisions that bring consequences. Many of these choices are subtle but have devastating consequences to the character's own lives and the lives of those close to them. It is a film that is about coming of age and the relationship between boys and father figures but it is also a film about such choices and, maybe, that people are not doomed to repeat bad choices throughout their lives.