Mr. Darcy's character contrasts dramatically with his counterpart, Elizabeth Bennet. His seriousness, arrogance, and obvious pride is ameliorated by her simplistic nature, her carelessness of social expectations, and her amiable character.
Yet, this contrast is a dynamic one; Darcy changes throughout the novel, shedding off the traits that elicited Elizabeth's on prejudice against him. In turn, the giving up of his pride in favor of his love for Elizabeth demonstrates that his own prejudice against Elizabeth's family and her class is as unfair as the prejudice that Elizabeth felt due to the lies that Wickham told her about Darcy.
Darcy's quiet demeanor and severe personality makes it hard for the reader to anticipate what are his real emotions, or predict what his next action will be. This is also an effective technique the readers as well as the characters to make inferences as to what is causing such behavior and what would be a way to counter act it.