Elias Disney became a legal US citizen in the 1930s, when he was in his 70s, after it was discovered he was still legally a Canadian citizen due to a technicality in his father's naturalization process.
Elias was born in Bluevale, Ontario, Canada, in 1859. His family moved to the United States and settled in Kansas when he was a teenager. His father, Kepple Disney, took out naturalization papers in 1879.
Under an Act of Congress at the time, minor children automatically became citizens when their father achieved citizenship. However, Elias had come of age (turned 21, the legal age of majority at the time) before the naturalization process was fully completed for his father. Unbeknownst to Elias or the rest of the family, this meant he legally remained a Canadian citizen.
The situation was discovered decades later, in the 1930s, when his voting status was challenged while he was living in Portland, Oregon. As a result, Elias and his wife Flora (who, having been born in Ohio, was also considered an alien due to marrying a non-citizen under the laws of the time) went through the formal naturalization process. He filed a Petition for US Citizenship in 1934. He was eventually naturalized by a judge, who noted that he did not have to go through the full procedure due to the circumstances.