The story of Kullervo is laid out in runes (chapters) 31 through 36 of the Kalevala.
Rune 31 – Kullervo, son of Evil
Untamo is jealous of his brother Kalervo, and the strife between brothers is fed by numerous petty disputes. Eventually Untamo's resentment boils into open warfare, and he kills all of Kalervo's tribe save for one pregnant woman named Untamala, who submits to Untamo. Shortly afterwards, Untamala gives birth to a baby boy she names Kullervo.
When Kullervo is three months old, he is heard uttering vows of revenge and destruction on Untamo's tribe. Untamo tries three times to have Kullervo killed (by drowning, fire and hanging). Each time, the infant Kullervo is saved by his latent magical powers.
Untamo then allows the child to grow up, then tries three times to find employment for him as a servant in his household, but all three attempts fail as Kullervo's wanton and wild nature makes him unfit for any domestic task. In the end, Untamo decides to rid himself of the problem by selling Kullervo into slavery to Ilmarinen.
Rune 32 – Kullervo as a shepherd
The boy is raised in isolation because of his status as a slave, his fierce temper, and frightening signs of early magical talent. The only memento that the boy retains from life in a loving family is an old knife that came along with him as an infant.
The wife of Ilmarinen enjoys tormenting the slave boy, now a youth, and sends Kullervo out to tend herd on her livestock with a loaf of bread with stones baked in it, along with a lengthy poem invoking the various deities to grant protection and prosperity to the herd.
Rune 33 – Kullervo and the cheat-cake
Kullervo sits down to eat, but the heirloom knife breaks on one of the stones in the bread. Kullervo is overwhelmed with rage, and, being unusually naturally gifted at magic, casts a curse that makes the cows Ilmarinen's wife is milking turn into bears, who kill her.
Rune 34 – Kullervo finds his tribe-folk
Kullervo then flees from slavery and finds that his family is actually still alive except for his sister, who has disappeared and is feared dead.
Rune 35 – Kullervo's evil deeds
Kullervo's father has no more success than Untamo in finding work suited for his son, and thus sends the young man to collect tributes due to the tribe. On the way back he meets a beggar-girl and seduces her without knowing or caring who she is. Afterward he realizes that she is his sister, and out of shame she commits suicide. The distraught Kullervo returns to his family to break the news.
Rune 36 – Kullervo's victory and death
Kullervo vows revenge on Untamo. One by one, his own family tries to dissuade him from the fruitless path of evil and revenge, and eventually rejects him, apart from his mother whose maternal love cannot be swayed even when she knows his course of action is wrong. Kullervo hardens his heart and refuses to reconsider, or even to pause to follow funeral rites when he hears his father, brother, sister and mother die in turns.
Kullervo goes on and obtains from Ukko his magic broadsword, which he uses to exterminate Untamo and his tribe. When he returns home, he finds the dead bodies of his own family littered about the homestead, untended. His mother's spirit gives him directions to woodland nymphs who can shelter him, but he finds instead the body of his sister, who committed suicide.
Kullervo then asks of Ukko's sword if it will have his life. The sword eagerly accepts, noting that as a weapon it doesn't care who it's used to kill. Kullervo commits suicide by throwing himself on his sword. On hearing the news, Väinämöinen comments that children should never be given away or ill-treated in their upbringing, lest like Kullervo they grow evil and bereft of wisdom or honor.
Kullervo is fairly ordinary in Finnish mythology, in being a naturally talented magician. However, he is the only irredeemably tragic character in Finnish mythology. He showed great potential, but being raised badly, he became an ignorant, implacable, immoral and vengeful man.
The death poem of Kullervo in which he, like Macbeth, interrogates his blade, is famous. Unlike the dagger in Macbeth, Kullervo's sword replies, bursting into song: it affirms that if it gladly participated in his other foul deeds, it would gladly drink of his blood also. This interrogation has been duplicated in J.R.R. Tolkien's The Children of Húrin with Túrin Turambar talking to his black sword, Gurthang, before committing suicide (also like Kullervo, Túrin unwittingly fell in love with his own sister and was devastated when he learned the truth).
Some literary critics have suggested that Kullervo's character is a bitter metaphorical representation of Finland's frequent struggles for independence. This proposal is contested. Certainly Jääkärimarssi (Jäger March), a well-known Finnish military march, contains lines me nousemme kostona Kullervon/soma on sodan kohtalot koittaa (We arise as vengeance of Kullervo/so sweet are the fates of war to undergo).
The story of Kullervo is unique among ancient myths in its realistic depiction of the effects of child abuse . The canto 36 ends in Väinämöinen stating that an abused child will never attain the healthy state of mind even as adult, but will grow up as a very disturbed person.
Kullervo in art
Kullervo is an eponymous 1860 play by Aleksis Kivi. An English translation was published in 1993: Aleksis Kivi's Heath Cobblers and Kullervo, translated by Douglas Robinson (North Star Press of St. Cloud).
There is also a Sibelius-inspired Kullervo Symphony written in 2001 by English composer Grahame Gordon Innes.
Kullervo is also the subject of a brief symphonic poem composed in 1913 by Leevi Madetoja.
In 2006 a Finnish metal band Amorphis released its seventh studio album Eclipse, which tells the story of Kullervo according to a play by Paavo Haavikko. The play has been translated into English by Anselm Hollo.