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)?

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.