"That book was made by Mr. Mark Twain, and he told the truth, mainly. There was things which he stretched, but mainly he told the truth" (1). Those are among the first lines in The Adventures of Huckleberry Finn, so it's obvious from the very beginning that the truth, or lack thereof, is a major theme in the book.
Huckleberry Finn is a liar throughout the whole novel but unlike other characters, his lies seem justified and moral to the reader because they are meant to protect himself and Jim and are not meant to hurt anybody.
Mark Twain shows four types of lies in The Adventures of Huckleberry Finn: vicious and self-serving lies, harmless lies, childish lies, and Huck's noble lies.
An example of lying is presented right at the beginning. After Tom and Huck play a joke on him, Jim lies to all the other slaves about how his hat got taken of his head and put on a tree limb above him while he was sleeping. He tells an incredible yarn about some kind of spirits visiting him, gaining him an almost-celebrity status among the slaves. Some may argue that this is a self-serving lie. Although it is harmless to others, it certainly isn't a noble lie. Another set of harmless, somewhat clever, lies Jim tells are of his famous hairball. He claims it can predict the future and only he can tell what it's saying. Not only that, but this hairball doesn't work unless Jim gets paid first.
The king of childish lies would definitely be Tom Sawyer. Through Tom's ridiculous lies, Mark Twain makes the reader begin to hate this impractical, unrealistic, unoriginal adolescent. His immature lies are to gain a sense of adventure like in his books and they occasionally hurt people. Tom tricks Huck into coming with him to see the caravan of "A-rabs and Spaniards." Huck doesn't want to go until he learns there will be elephants there too. They go, and of course, nobody is there but young, Sunday-schoolers. Huck is disappointed and says, "So then I judged that all that stuff was only just one of Tom Sawyer's lies" (14). Tom's major lying, though, doesn't start until chapter 33 and doesn't end until the last part of the book. When asked to help Jim escape, instead of saving weeks and weeks of trouble by telling Huck that Jim is already free, Tom has to glorify rescuing Jim. He frightens the whole Phelps family and 15 men with shotguns through his childish games. He gets shot and puts poor Jim through all sorts of obstacles. His lying is definitely not portrayed as positive in any way.
The most negative liars in the whole novel, though, are the Duke and the King. They are accomplished con-artists who make it their life to lie and trick the naïve public out of their money. In fact, they are introduced to Huck and Jim while they are fleeing from an angry mob: one for selling a paste to remove tartar from teeth that takes a good deal of the enamel off with it and the other because he was caught drunk after running a temperance sobriety revival meeting. Every lie of theirs is completely self-serving and wicked. The Duke and the King are truly antagonists because they are able to betray everyone, including the people who save them and take care of them, Jim and Huck. When their cons don't work well, they sell Jim to the Phelps, telling them he is a runaway. But to the Duke and the King's knowledge, Jim belongs to Huck. When Huck questions the Duke about Jim's whereabouts, he slips and says the Phelps' farm, but quickly lies and says Jim's on a farm 40 miles down the road. The other very despicable string of lies they tell trick three young daughters out of their deceased father's 6000 dollars and all his property; That is enough for Huck.
It is true that Huck Finn is so accustomed to lying Jim and himself out of trouble that he says, "I reckon a body that ups and tells the truth when he is in a tight place, is taking considerable many resks, though I ain't had no experience, and can't say for certain"...