Aaron Hotchner

Hotch's personality has changed very little over the course of the show. He has always been extremely serious, determined, and focused on his leadership of the team, never seeming to waver or lose sight of the task ahead, barely allowing his dry wit and humor to appear. However, the events surrounding George Foyet's final appearance did cause him to become temporarily single-minded and obsessive to the point where he would appoint Morgan as Unit Chief for a short period of time. He was especially grim and didn't smile at all during this time. Outside of work, especially while interacting with his loved ones, his seriousness abates and the more carefree, good-natured, and good-humored side of his personality shows up, transforming his countenance to a point that people who know him little get a hefty surprise.