The ironic guard
The German guard who frees David is an ironic character, because Nazis represent human depravity, hatred, and malice, but the guard demonstrates the opposite of all that. He helps David, he makes a way for him to escape, and he puts him on a path to find his mother. The guard is a hero in this novel too, because he loved the "enemy" and was moved to help.
The painful hero
David is an ironic hero, because he is both a savior (he saves Maria from a burning barn), but he is also kind of a painful hero to live with, because the truth about David's story is so heartbreaking and disturbing that whoever meets David loses their innocence in the encounter. The family worries about his effect on Maria's developing psychology, and he leaves. This irony resolves nicely when his mother embraces him. She understands his suffering, because she also escaped a Nazi concentration camp. He is finally understood.
The unlikely reunion of David and his mother
David is reunited to his mother at the end of the novel. This is ironic because the reader (and David) are led to believe that his mother is dead. David assumes this, because he is an orphan in a concentration camp, but ironically, he learns halfway through his journey to Denmark that his mother is alive and well, living in Copenhagen. When he gets there, he simply finds her in the phone book and calls her.
The painter's ironic story
When David has his portrait drawn by a painter, he sees a painting of his mother, but he doesn't really know that exactly; rather, he feels a deep sense of longing and attachment to the woman, but when he hears the irony of the painter's story, he suddenly knows the truth. The painter thinks that the woman's son, David, was killed in a concentration camp, but that this woman escaped because of the kindness of a German guard. David realizes that he must be the missing son from the story.
The irony of David's biblical life
A Jewish reader would notice that David's journey through Europe has important similarities to the story of his namesake, King David from the Jewish scriptures. In those stories, David starts as a disenfranchised, mistreated youth who ends up being pursued by those who want to kill him. Both Davids live in paranoia. Both of them are in life-threatening situations where soldiers want to find them and kill them. Both of them find refuge in a cave. This is highly ironic, because one of the most important parts of David's life in the concentration camp is that although he is a Jew by ethnicity, he hasn't been taught any of those stories. He discovers his Jewish identity by living through a story that is astonishingly similar to Biblical Old Testament stories.
