Zoltan Papp, who represented Barber in his legal case following his 2019 arrest, says he and the former Dallas Cowboys running back were close friends -- and the 38-year-old had given him no signs recently that he had been in any kind of trouble.

"There was no indication of any desire to end his life, if that is what happened," Papp said. "Everything was about the fight to bring justice and to help others. Marion is a person who at his core is pure good."

Papp tells us Barber -- who was found dead in his Frisco, Texas apartment on Wednesday afternoon -- had started a trucking venture following his retirement from the NFL after the 2011 season.

Papp also says the former Pro Bowler was an advocate for social justice and had spent a large portion of the past few years trying to help kids in inner cities.

In fact, Papp tells us the ex-tailback was involved in the coaching team at Flow -- a business simulation designed to help people improve their leadership abilities and lifestyles.

Barber was also working on a book about his life "to show others how to work through difficult times," Papp added.

"He has been a warrior for all in a constant battle with an unjust system," Papp said. "He attacked his craft of football and life with grace, integrity, purpose and authenticity."

"He lived life humbly and with kindness and generosity ... and all against a system that gave little help or support, and recently went hard against him as he was working on helping others."

As for any effects of potential CTE, Papp said, "Marion's personality is grounded as a very humble and soft-spoken man, and that may be wrongly taken as cognitive dysfunction."

Authorities have yet to release any information regarding the circumstances of Barber's death. Cops say an investigation is still ongoing.