Thomas B. Hofeller achieved near-mythic status in the Republican Party as the Michelangelo of gerrymandering, the architect of partisan political maps that cemented the party’s dominance across the country. After he died last summer, his estranged daughter discovered hard drives in her father’s home that revealed something else: Mr. Hofeller had played a crucial role in the Trump administration’s decision to add a citizenship question to the 2020 census. Mr. Hofeller seemed a bystander in the citizenship-question debate, mentioned but once in thousands of pages of lawsuit depositions and evidence. Proof of his deeper involvement surfaced only recently, and only after a remarkable string of events beginning after his death in August at age 75. Mr. Hofeller was survived by a daughter, Stephanie Hofeller, from whom he had been estranged since 2014. In an interview, Ms. Hofeller said she learned of her father’s death by accident after searching for his name on the internet, and returned to her parents’ retirement home in Raleigh, N.C., to see her mother, Kathleen Hofeller.