Sophocles' play Antigone most definitely has the characteristic Aristotle defines as "character consistency." Aristotle asserts in his Poetics that one aspect of a well-written tragedy is that it must have a consistent protagonist. As Barbara F. McManus translates, "Once a character's personality and motivations are established, these should continue throughout the play" ("Outline of Aristotle's Theory of Tragedy in the Poetics").
We learn at the very beginning of the play what Antigone's personality and motives are. Antigone is very strong willed. Plus, she is insisting on burying her brother for a couple different motives: 1) She believes wholeheartedly in being loyal to her kindred, as we see in her lines addressed to Ismene, "I'll bury my brother--your brother, too, though you refuse! I'll not be found a traitor; 2) She believes that the laws of the gods are higher than the laws of man, such as Creon's laws. We especially see Antigone assert her view that the gods' laws are above man's when we see her argue to Creon in her defense:
I would never think your pronouncements had such strength that, being mortal, they could override the unwritten, ever-lasting prescriptions of the gods ... I did not intend to pay the penalty to the gods for violating these in fear of some man's opinion. (462-470)
Throughout the rest of the play, Antigone remains strong in these convictions. Even when the chorus begins to chastise her for being too strong-willed, she does not change her mind. Hence, we see that like Aristotle asserts, Antigone is a consistent character, which is one point that makes the play Antigone a well-written tragedy.