In Clive King's children's novel "Stig of the Dump", who or what is Stig?

"Stig of the Dump" is probably the best known work of the English author (David) Clive King (1924-2018).

First published in 1963, it tells the story of Barney, a young boy who is finding a holiday spent with his grandparents decidedly tedious, and when he is out exploring he tumbles into an old chalk tip, where he meets Stig, a shaggy-haired caveman. Barney is not afraid of Stig, and the two become friends, communicating with each other despite Stig's inability to speak English. Barney helps Stig to make the pit more hospitable by clearing the rubbish that has accumulated there. But the local bullies, the splendidly named Snarget brothers, are overawed by him. However, unlike others, they do believe in his existence.

On Midsummer's Eve, Barney and his sister find themselves transported back in time to Stig's era, and join in with the construction of four giant standing stones, as the past and present fuse.

The novel has been adapted several times for stage and screen, and has even formed the basis of a computer game.