Julius Erving got his nickname "The Doctor" from a friend who played pickup games with him back in Roosevelt, Long Island. Julius called his buddy "The Professor" becaus
…e he was always very talkative and argumentative on the court and gave long drawn out explanations for why he was always right with his calls. One day his friend returned the favor and called him "The Doctor" because of the way we could slice through defenses and "operate" on his opponents especially in a one on one situation. It was later shortened to Dr. J. by his Virginia Squires teammates in the ABA and it caught on with fans and kids. He would also sometimes be referred to as just "Doc." (MORE) 
