Obligation of Reciting Kaddish for Parents

Is it obligatory to recite Kaddish and lead the prayer service for one's father during the first year of mourning?

There is an obligation to recite Kaddish as part of the commandment to honor one's father and mother. Among Ashkenazim, it is also customary to lead the prayer service (and serving as the prayer leader is considered more important than reciting Kaddish).

In Beit Yosef, Yoreh De'ah, Siman 376, a story from the Midrash mentioned in Tractate Kallah is brought: "The Kol Bo (p. 88) writes about what is found in the Haggadah that once Rabbi Ploni (and in early sources it is mentioned that it was Rabbi Akiva) encountered someone gathering wood and carrying it on his shoulder. He asked him, 'My son, why do you do this?' He replied, 'Rabbi, this is my judgment for all days, to bring into the fire of Gehinnom and be judged there.' He said to him, 'There is no one to save me unless my son recites one Kaddish or reads a passage from the Prophets.' (In early sources, the continuation of the story is brought, that Rabbi Akiva went and circumcised his son, taught him to pray, and he recited Barchu and Kaddish, and the deceased appeared to him and said that he was saved from the judgment of Gehinnom.) Based on this, the custom spread for the son of the deceased to recite the final Kaddish for all twelve months and also to read from the Prophets, and some pray the Arvit prayer every Saturday night because at that time the wicked return to Gehinnom, and perhaps that prayer will protect them. [End of quote] This story is also found in the Zohar Chadash at the end of Parashat Acharei Mot. And since we find that Kaddish saves the father from Gehinnom, it is considered honoring one's father and mother, as we find in Kiddushin that he honors him after death, and says, 'I am the atonement for his rest,' meaning he asks that through the sufferings the son endures, the father will be released from Gehinnom. And therefore, it is the same when he releases him from Gehinnom through his efforts to recite Kaddish. The Rema writes in Siman 376, paragraph 4: 'On weekdays, one who knows how to pray should pray, and it is more beneficial than the Orphan's Kaddish, which was only established for minors.' And see in Birkei Yosef, Siman 240, paragraph 8, where it is written that it is merely a custom, and not an absolute obligation. Some write that it is a Torah obligation of honoring one's father and mother. And some write that even if we say it is merely a custom, nevertheless, once the custom has taken root, one who cancels it transgresses the disrespect of his father.