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?