After his father died, Mark Charles Roudané, a retired Minnesota schoolteacher, began going through his dad’s papers. There were scores of binders, the records of a life as a prosperous, white, Presbyterian businessman in the Midwest.

All of the files were labeled — except one. When Mr. Roudané, 55 years old at the time, opened the unmarked folder, he found an old photograph of a Black man named Dr. Louis Charles Roudanez.

Dr. Roudanez, a wealthy physician in New Orleans who co-founded two of the earliest Black-owned newspapers in the United States, was Mr. Roudané’s great-great-grandfather.

“In an instant, my identity shifted.”

The news that Robert Francis Prevost, the Chicago-born cardinal who became Pope Leo XIV, had family roots among New Orleans Creoles has enthralled few people as intensely as those who share his heritage. While members of the pope’s immediate family identified as white, various records from New Orleans from just a generation earlier describe his maternal grandparents as “mulatto” or Black. Such a story is a curiosity for many who are unfamiliar with Creole culture. But for those with Creole roots, there is something immediately familiar about it.

“Anyone who looks at me outside of New Orleans sees my street race, which is white,” said Mr. Roudané, now 73, using “street race” to describe the perception of a person’s heritage that people draw from a quick glance. “Anyone who looks at me in New Orleans looks at me and goes, ‘OK, I see where you’re coming from.’”