Dr. Aurelius was a Rebel doctor who was to take care of Katniss Everdeen during her stay in District 13. Dr. Aurelius was native to 13 and was happy to get Katniss as his patient as she would not cooperate with him exactly so he saw his sessions with her to be opportunities to take naps to make up for all his sleepless nights during the war.
Dr. Aurelius was also the doctor who was heading the study on Peeta's hijacking, sampling his memories with archived footage of his past with Katniss, his family, even bringing in some witnesses to help him regain his old thoughts. Though most of Dr. Aurelius' actions did not seem to make a difference as Peeta's recovery only helped when he was with Katniss himself in person, not through the doctors methods.
After Katniss assassinated President Coin, Dr. Aurelius was summoned to her trial where he deemed her a mentally unstable lunatic to save her from facing execution at the hands of District 13's government. In the end she was sentenced to being confined to the ruins of District 12 and she had to keep in contact with Dr. Aurelius to monitor her "mental illness". As Katniss wasted months in 12 Dr. Aurelius covered for her not calling by making up fake records and pretending to be treating her until she finally did contact him.