This is the 11179th most frequent Russian word.
грекам
The word "грекам" is the dative plural form of "греки," meaning "to the Greeks" or "for the Greeks."
Here, 'грекам' is in the dative plural form, indicating the indirect object receiving the book—the Greeks.
Я подарил книгу грекам.
I gave a book to the Greeks.
In this sentence, 'грекам' is also in the dative plural and relates to attribution, referring to the Greeks as those to whom the creation is credited.
Грекам традиционно приписывают создание Олимпийских игр.
The Greeks are traditionally credited with creating the Olympic Games.
Again, 'грекам' is in the dative plural, referring to the recipients of the information—the Greeks.