Though Twain tells us that Huck's father is the "town drunkard," Muff Potter certainly gives Mr. Finn a run for his money. Indeed, Muff's drunkenness leads him to take up a life of crime with Injun Joe, and nearly get hanged in the process. In his sorry state, he barely knows what's going on. When Injun Joe lies and says Muff has stabbed Dr. Robinson to death, Muff doesn't put up a fight. Instead, he blames his supposed actions – and his inability to remember them – on his drunkenness, and asks Injun Joe not to rat him out. But Injun Joe does just that.
Muff is certainly the most pitiful character in Tom Sawyer, and his plight gives Tom and Huck the opportunity to demonstrate their kindness and compassion. They visit him in jail, bring him gifts, and, eventually save his life. All Muff can do is thank them and warn them to avoid drinking alcohol. In the end, that's enough. Twain invests him with enough pathos – a fancy Greek word for pitifulness that we literary types like to use – that Muff Potter sticks with you long after the plot has left him behind.