Boris is the witch Griselda’s pet skull
He is strangely fond of her (the stories do not reveal why) but she gives him a very hard time, sending thunderbolts which echo in his bony head and kicking him out of the window.
The basic problem with Boris (accordingly to Griselda) is that he is not evil enough. Indeed, she sometimes thinks that he is not evil at all, which is odd in a floating skull which ought to have all the powers of evil. Griselda would like a skull which floats through the forest zapping people with his laser beam eyes, but all Boris does is play harmless tricks. This makes Griselda very cross (she also thinks that having a skull who says he loves her is ugh, really soppy). Griselda would like to recondition Boris to make him evil.
What Boris would like is to get back his body. He cannot remember much about life before he was captured by Charlie Stench, the Body Collector (who added his body to his collection and turned the head into a floating skull) but he misses not being able to dance and swim. He wants his body back so much it makes him really unhappy until finally fed up with Griselda (who is a frightful bully) he decides to form a punk rock band, Boris and the Dumb Skulls, with Griselda’s guards the Dim Daft Dwarves. Even that ends up with Griselda bouncing him from wall to wall, from floor to ceiling and finally (with a yell of fury) burying him deep in the earth (where the Dim Daft Dwarves have to dig him out).