Of the two scoundrels that accompany Huck on his Mississippi River journey in Mark Twain's The Adventures of Huckleberry Finn, the duke seems to show a better degree of friendliness and intelligence.

LIKABLE.  After the gold is discovered in the coffin and the two scoundrels have caught up with Huck and Jim, the king threatens Huck. But the Duke realizes that Huck is telling the truth (mostly) and stands up for him:

"Leggo the boy, you old idiot! Would you 'a' done any different? Did you inquire around for him when you got loose? I don't remember it."

CAUTION.  The duke shows his cautious side when he tries to convince the king to be happy with the gold and make their getaway.

The duke, he grumbled; said the bag of gold was enough and he didn't want to go no deeper--didn't want to rob a lot of orphans of everything they had. 

INTELLECT.  The duke comes up with the excuse to use in case Jim is identified.

"Whenever we see anybody coming we can tie Jim hand and foot with a rope, and lay him in the wigwam and show this handbill and say we captured him up the river, and were too poor to travel on a steamboat, so we got this little raft on credit from our friends and are going to get the reward."
    We all said the duke was pretty smart...