Is characterization what the character does to portray a theme?
Characterization is when the author describes a character, sometimes directly and sometimes indirectly, to help the reader become acquainted with the character, his habits, and his personality.
Direct characterization is when the author simply tells the reader a trait. For example, "he was a quiet person" would be direct characterization.
Indirect characterization is when the author gives the character's words and actions, and from those the reader infers his personality. An example would be "his eyes gleamed with evil glee as he slowly burned the the little bug." The reader can logically infer that this boy enjoys cruel entertainment.