There seems to be an issue as to who his parents are. One theory is Hans Georg Dillman and Margaretha Muirr. The other theory is Andrew/ Dillman and Barbary Roush.
I've checked Ancestry and most trees show him as the son of Andrew, which is probably based on a book "Genealogy of the Houser, Rhorer, Dillman, Hoover Families", 1910, by Dr. WW Houser. However, a notation on his Find a Grave states this has been disproven through DNA and that the book is not documented.
The oldest record I could find for him was in 1790, but he was already 40 years old, so it doesn't link him to any parents.
I did find an immigration record for Hans George. The U.S. and Canada, Passenger and Immigration Lists Index, 1500s-1900s lists his arrival in Philadelphia in 1751 with a wife and two children. Andrew was born in 1751, supposedly in Pennsylvania. It doesn't really prove anything, but I really couldn't find any records for his supposed father Andrew.
Who are his parents?