I found this interesting Hotch biography on IMDb. Enjoy!

FBI Behavioral Analysis Unit Supervisory Special Agent/Unit Chief Aaron "Hotch" Hotchner is played by Thomas Gibson.

Hotchner is the head of the BAU team. Hotchner was a prosecutor for a time, although it is not stated specifically where, his experience in prosecution helps his team to craft tight cases, it also allows him to judge when (and how) it may be necessary to skirt the law to successfully capture and prosecute an UNSUB (unknown subject). He is often referred to as a drill sergeant he very rarely smiles and it is a common joke...