Q. Can a Ger recite Kaddish for his dear father that did not convert, but was very good and helpful to him, practically from the ‘ Chasidei Umot Haolam’, (righteous of the nations)?
A. Z’kan Aharon (2; 86) maintains that although it is for many a surprising tradition, it is proper in such a case to recite Kaddish for his Gentile father, although it is not an obligation.
Mimamakim (3: 8) deals with reciting Kaddish for a non-Jewish woman, that saved the life of many persecuted during W.W.11.
Horav Shlomo Miller’s Shlit’a opinion is that Kaddish should not be recited.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a.