The Nun's Priest's Tale is a fable that allegorical. Though the characters are animals, the animals represent elements of human nature and the ultimate goal of the tale it to reveal a "universal truth" about human nature.
Chauntecleer is best characterized by his physical appearance and abilities. You must also consider what characteristics are alluded to by the choice of animal, a rooster or cock, for the main character in the fable. When one thinks of a rooster, the descriptors often associated with this animal are egotistical, overly confident, and arrogance. In addition to the stereotypical character traits associated with a cock, we are told by the narrator that Chauntecleer is a prized cock because
"In all the realm of crowing without peer.
His voice was merrier than the play
Of the church's organ each holy day" (2850-2852).
He is also described as physically handsome
"His bill was black and like the jet it glowed,
His legs and toes like azure when he strode.
His nails were whiter than the lilies bloom," (2861-2863).
These traits ultimately cause Chauntecleer to ignore his beliefs that his own death is foretold in his dream. Although the narrator would contend that Chauntecleer's mistake was taking "his wife's advice, to his dismay"(3253), it is truly his belief that he is so wonderful and rare that he will be unharmed that leads to his fatal mistake. This is evident when Chauntecleer sings for the fox because of the fox's flattery.
"This Chanticleer would not have tarried more
Once he espied the fox, had not the latter
Said, "Gentle sir, alas! what is the matter?
I am your friend--are you afraid of me?
I'd be worse than a fiend, most certainly,
To do you harm. And please don't think that I
Come here upon your privacy to spy;
The reason that I've come is not a thing
Except that I might listen to you sing.
For truly you've a voice as merry, sire,
As any angel's up in heaven's choir.
Because of this, in music you've more feeling
Than had Boethius, or all who sing" (3282-3294).
As a result of Chauntecleer's ego, he is easily captured by the fox and taken off into the forest. Once there, we "For see how Fortune upsets suddenly /The hope and pride now of her enemy!" The fox's ego results in Chauntecleer's freedom because the fox cannot help but brag about his fortune. When the fox tries to entice Chauntecleer a second time, the cock will not be fooled. He tells the fox, "You shall no more, with words so flattering,/ Inveigle me to close my eyes and sing." He has learned his lesson.
As a result, Chauntecleer may be considered a round character in the Nun's Priest's Tale because he learns from the errors of his ways and is not a victim of his ego a second time. A round character is one who develops throughout the course of a text; a static character remains unchanged.