The Black Giant is the central villain of the Serbian fairytale The Biter Bit, he is a classical fairytale monster who must obey certain rules in his dealings with humans but often exploits them to his own advantage, being an evil sorcerer as well as a formidable giant: he is never named in the story but gains his title both from his physical appearance and his malicious nature (in folklore, malicious magic, for example, is often known as "black magic" or simply "evil magic", though in modern times it tends to be called "dark magic").
The Black Giant is first encountered when he magically traps an entire party of people going to celebrate a marriage, transforming the bridge they were crossing so they couldn't pass nor even move from their position: he offered to set them free in the old man (who had brought them there) agreed to surrender to him the one thing he left at home, the old man agreed and the giant told all present that they were witnesses to the agreement, freeing them.
Later the old man is horrified to learn the one thing he had left at home during the festivities was his eldest son, soon the Black Giant arrives and demands his payment - he proceeds to take the old man's son as a servant but says the old man may come to him in three years time and have his son back.
For 3 years, the old man lives in misery and despair over the loss of his son, whom the Black Giant teaches in dark magic - after the time passes he rushes back to find the Black Giant and reminds him of their agreement.
The Black Giant proceeds to produce a plate with three different birds on it, telling the old man if he can determine which bird is his son he may be set free - this task seems impossible and the old man becomes more upset each time.. the Black Giant finds this all rather amusing, clearly having never truly intended to allow the old man his son back.
After the second attempt to find his son fails the old man is approached by an old woman who asks what is ailing him, upon explaining his situation the old woman tells him to look for a bird whose eyes have tears - that bird would be his son : the old man, with renewed purpose, did just that and upon the third attempt successfully found his son.
The Black Giant had no choice but to allow father and son to go free after this and for some time they were not troubled by him again, until he learned that the old man's son was now using magic the giant had taught him to gain wealth for himself and his family : jealous of this he manages to capture the boy again and the two engage in a lengthy shape-shifting battle that ultimately ends in the boy slaying the evil giant and freeing himself once and for all from the monster: the boy then returned to his father, who he made very rich - thus earning the fabled "happily every after" of all fairytales.