No. Robert Ludlum is not Jewish.
Robert Downey, Jr. is of three eighths Jewish ancestry. Robert's paternal grandfather was the son of Lithuanian Jewish parents. Robert's paternal grandmother was the daughter of a father of Irish (non-Jewish) descent, and of a Hungarian Jewish mother. Robert's mother was not Jewish. Robert is married to a Jewish woman. (Note that the above refers to ancestry, not religion. In Judaism, one's religion is determined by that of the mother [except for converts]).
The American economist Robert Shiller is not Jewish. Robert Shiller is of Lithuanian decent. Robert was born in Detroit, Michigan on March 29,1946.
Robert Lansing was raised as a Presbyterian but later in life he did not have a strong affiliation with any specific religion.
Robert Schumann was German.
No.
Yes
He is Jewish.
Yes
Yes.
yes
Yes