EXCLUSIVE

The passenger who was savagely removed from United flight 3411 is a medical doctor with a sordid history.

Dr. David Dao was charged in 2005 with 98 felony drug counts for illegally prescribing and trafficking painkillers. Prosecutors claimed Dao fraudulently filled prescriptions for hydrocodone, Oxycontin and Percocet.

Dr. Dao was also convicted on 6 felony counts of obtaining drugs by fraud and deceit and in 2005 was given 5 years probation.

Dao was also convicted for writing prescriptions and checks to a patient in exchange for sex.

In medical board documents ... Dao denied paying for sex, but indicated he accepted sexual favors from an associate in exchange for reducing a debt that associate owed him.

In February, 2005, Dr. Dao surrendered his license to practice medicine in Kentucky. In 2015 the medical board lifted the suspension and allowed him to practice medicine with some restrictions. Last year, the medical board imposed even more restrictions -- now he can only practice internal medicine in an outpatient facility one day a week.

Interestingly, and relevant to the United incident, one doctor assessing Dao's case said he had interpersonal problems, noting "... he would unilaterally choose to do his own thing."