He endorsed numerous products, including a video game series.

Freestyle BMX is a dangerous sport that produces many crashes, and Mirra was involved in many. In a 2006 crash, he told The Washington Post, “I basically fell 16 feet straight to my head.” He was also hit by a car at age 19, breaking his skull.

Mirra died from a self-inflicted gunshot in February in Greenville, N.C. He was 41.

C.T.E. can be diagnosed only through a brain examination after death. Dozens of football players have been found to have had it, including Frank Gifford, Junior Seau and Ken Stabler.

The disease can affect memory, cognitive function and mood.

“I started to notice changes in his mood,” Mirra’s wife, Lauren, told ESPN. “And then it quickly started to get worse. He wasn’t able to be present in any situation or conversation, so it was hard to be in a relationship with him to any degree.”

The Mirra family, like many families of former N.F.L. players, decided to pursue posthumous brain testing to learn if he had the condition. Lauren Mirra said the family planned to start “a platform for C.T.E. awareness and research.”