BsD B"H Shalom UVracha & Bsorot Tovot B"H! If a person receives an info that this persons non-jewish biological father (this persons mother is Jewish, this person was raised since the childhood by mothers another Jewish husband whom this person sees as the father, but knowing that this is not the biological father) has passed away a number of years ago (there was no contact to the biological father, no relationship since the cildhood), is this person obligated to do / to keep something regarding that a number of years later? What / which things would be allowed to do, what could be done? Shkoyach and thanks a lot in advance for the reply! B"H Rak Bsmachot, Rak Bsorot Tovot VeKol Tuv B"H!

This person has no obligation of mourning or the like (Shulchan Aruch, Yoreh Deah 374:5). Expanded Discussion From a halachic perspective, the child is not regarded as the son of his non-Jewish father. Therefore, he is not required to observe the laws of mourning for him. Some authorities maintain that it is appropriate for a convert to recite Kaddish for his non-Jewish father, since his father brought him into this world, where he ultimately merited to observe Torah and mitzvot. However, there is no obligation to recite Kaddish for one's father (see Yechaveh Da'at, vol. 6, no. 60). Likewise, Responsa Zeken Aharon (vol. 2, no. 87) writes that there is room to argue that a convert should recite Kaddish for the elevation of his father's soul, although in practice he did not obligate him to do so. On the other hand, Rabbi Mordechai Eliyahu of blessed memory ruled that there is no benefit in a convert reciting Kaddish for his non-Jewish father, because Kaddish has the power to elevate a Jewish soul from one spiritual level to another, whereas a non-Jew remains at his own spiritual level. At most, he said, one may recite a memorial prayer (Hashkavah), asking that Heaven have mercy upon him. Similarly, Mishneh Halachot (vol. 19, no. 155) rejects the view of Zeken Aharon and writes that it is clear that a convert should not recite Kaddish for the elevation of his non-Jewish father's soul. He adds that, were it not for his hesitation, he would even suggest that doing so could call attention to the father's shortcomings, since he had a son who came to recognize his Creator and entered beneath the wings of the Divine Presence, yet the father remained steadfast in his own path. He compares this to the verse, "Have you come to remind me of my sin?" (I Kings 17:18). Mishneh Halachot further writes that if a convert's parents also converted, and his father raised him from childhood, then there are two reasons for the son to recite Kaddish: his father both brought him into the world and raised him. In such a case, it is possible that the son would indeed be obligated to recite Kaddish after his converted father. It would appear that this entire discussion regarding whether a convert should recite Kaddish for his non-Jewish father also applies to a child born to a Jewish mother and a non-Jewish father, as in the present case. In our case, however, there is an additional reason not to recite Kaddish: from the question it is clear that the biological father did not raise the child at all, the child did not know him, and there was no relationship between them. Nevertheless, if the son wishes to do something in appreciation of the fact that his biological father brought him into this world, it would seem appropriate to follow the suggestion of Zeken Aharon, who writes: "In my opinion, any convert who is hesitant to recite Kaddish publicly may instead study Torah and recite Psalms in its place. In either case, if this brings spiritual benefit to his father's soul, all the better; and if not, his Torah study will certainly remain a source of holiness and merit for himself." Alternatively, following the ruling of Rabbi Mordechai Eliyahu, he may recite a Hashkavah prayer, asking that Heaven have mercy upon his biological father.