My German born ancestor was George Trautvetter–born in the 1790s. He had brothers Adam, Michael. and Henry. I was years into researching the family before I learned that at least two of them really had the first name of John or Johann–using that first name combined with the middle name made finding them easier. They dropped the “first name” after a while in the United States, but used it on passenger lists and records early in their settlement.
Is your ancestor hiding under an “unknown” first name?