All his life, Cleon Brown, a 47-year-old police sergeant in Hastings, Mich., had thought he was a white man with some Native American blood.

But whenever people heard his name, Cleon, which he shared with his father, they would assume that he was a black man. He became a little suspicious of his actual heritage when his daughter, now 18, was given a diagnosis at birth for an illness that he said was typically found in African-Americans.

Ever curious about his background, he decided to take a DNA test from Ancestry.com last year. The results were surprising: He had zero Native American blood in him, but was 18 percent sub-Saharan African.

But Sergeant Brown said, “I was so proud of it,” in describing the moment that his wife called him at work and told him about the test result.

The clarity was relieving. He proudly told his colleagues at the police department, he said. But not long after that, his elation turned into misery.

“Kunta,” the Hastings police chief, Jeff Pratt, said to Sergeant Brown at the station one day, according to a federal civil rights lawsuit that the sergeant filed last month.

Later, the lawsuit charges, some members of the department “started whispering ‘Black Lives Matter’ while pumping their fists as they walked” past Sergeant Brown. Even the mayor at the time, Frank Campbell, got in on the racist teasing, Sergeant Brown said, by telling him a joke in which he used the word “Negroid” at least twice.

And last December, a fellow sergeant stuffed his Christmas stocking at the station with a black Santa figurine that had “18%” written on its beard, according to the complaint.

The city disputes the charges, saying that it was Sergeant Brown who started joking about race after receiving the test results.

But he insists that he was taunted. That made all the tension between police departments and black communities that Sergeant Brown had seen on the news feel more real and relevant to him than he had ever imagined. …

He is seeking at least $500,000 in his lawsuit against several city and police employees, but he says that most members of the department have been supportive. …

But the city said it was Sergeant Brown who fueled the banter by joking with his colleagues about the results, in a statement released by its lawyer, Michael S. Bogren.

According to the city’s statement, Sergeant Brown said that he now understood why he “likes chicken so much,” and that “the 18 percent is all in my pants.” …