There are many words that describe Tom Sawyer. So, my list will have to be selective. Here are three words and quotes to back them up.
First, Tom is crafty or mischievous. He can make others do his work for him as he manipulates them. For example, he makes whitewashing a fence something fun in order to make another boy do his job for him. He says to this boy: "Does a boy get a chance to whitewash a fence everyday?"
Second, Tom is a boy. In fact, he is all "boy." A nice window into his life is when he feels hurt that Becky does not like him. His feelings are telling of his youthfulness.
"Now as to this girl. What had he done? Nothing. He had meant the best in the world, and been treated like a dog -- like a very dog. She would be sorry some day -- maybe when it was too late. Ah, if he could only die temporarily!"
Third, Tom is also heroic as he testifies about the murder of Dr. Robinson. What makes this complicated is that it was Tom's mischief that enabled him to witness the murder. But in the end, he was heroic.
"Tom was a glittering hero once more—the pet of the old, the envy of the young. His name even went into immortal print, for the village paper magnified him. There were some that believed he would be President, yet, if he escaped hanging."
In the end, Tom matures.