Marvin Thompson, a crucial inspiration to his younger brother Jam Master Jay, and one of the primary keepers of Jay’s flame in the years since his murder, died at Vidant Medical Center in Greenville, North Carolina, on November 29. The cause was complications from sickle cell anemia, according to Kimba Reynolds, chief operating officer of the Jam Master Jay Foundation for Youth, which Marvin and his mother co-founded in 2003. He was 63 years old.

Soft-spoken and self-effacing, with a sly sense of humor, Marvin had style to burn. It was only natural that Jason Mizell—the young musician who would become Jam Master Jay—took fashion cues from his older brother. “Jay always wanted to dress just like Marvin,” says Jay’s friend and schoolmate Smith. It was Jay’s flair, in turn, that defined Run-DMC’s look and the group’s fashion sense, which pivoted the whole of hip-hop away from interplanetary fantasy and towards the gangster panache then on parade in the streets of Queens.

Specifically, when Jay began wearing Stetson Godfather hats as a junior-high-schooler, he did so in emulation of Marvin, who was 10 years older. Marvin once told this reporter that he himself had been influenced not only by Marlon Brando in the title role of The Godfather, but by Edward G. Robinson in Little Caesar. “I’m a big Edward G. Robinson fan,” he said.

Marvin L. Thompson was born in Brooklyn, New York, on December 9, 1954. He was a member of Run-DMC’s road crew during the group’s early barnstorming years. Andre “Doctor Dré” Brown recalls rolling with Marvin during the Raising Hell Tour in 1986. The photographer Ricky Powell says Marvin was part of the posse on the Together Forever Tour in 1987.

In the wake of Jay’s murder in 2002, Marvin formed the Jam Master Jay Foundation for Youth. From the beginning, he worked alongside Kimba Reynolds, who he’d known from her years as a pioneering female rapper. A community organization based in Hollis, the foundation provides books to schools and sponsors annual events, donating turkeys on Thanksgiving and toys for kids during the Christmas holidays. It was also through the foundation that Marvin spearheaded the renaming of the intersection of 205th Street and Hollis Avenue in Hollis as Run-DMC-JMJ Way in 2009.

2009 was also the year that Run-DMC were inducted into the Rock and Roll Hall of Fame. The Hall of Fame provided Jay’s wife with tickets to the ceremony, but neglected to invite Connie Mizell-Perry, Jay’s mom. It was Mizell-Perry who had opened her house to Run-DMC in their very earliest days, literally giving them a place to get their act together—a vital display of generosity and encouragement. Undeterred by the Hall of Fame’s oversight, Mizell-Perry and Marvin traveled together to Cleveland, dressed themselves to the nines, and bum-rushed the red carpet. They ended up sitting at Run-DMC’s table and took the stage with the others to accept the crew’s award.

Marvin moved to Winston-Salem, North Carolina, earlier this fall to care for his mother following the death in July of his and Jay’s sister, Bonita Jones, who herself had moved down South for the same reason.

Marvin was a lifelong member of the Omega Psi Phi fraternity, which he joined as a biology major at Long Island University in 1981. He is survived by his daughter, Priscilla Thompson, and his mother, Connie Mizell-Perry.

Although the murder of his brother, Jam Master Jay, remains a “cold case,” Marvin continued through the years to cooperate with the New York Police Department’s ongoing investigation in the hope that the case would indeed be solved someday.