Stephen Blackpool is by far one of the most interesting and tragic characters in this great novel. Consider how he is introduced: we only meet him after Dickens has shown us the Gradgrind family and Bounderby, and of course the juxtaposition of the Gradgrinds and Bounderby with Stephen and his life creates a sharp contrast to these earlier characters. Stephen is not a rich member of Coketown society, but he is instead one of the "Hands" in Bounderby's factory whose life consists of poverty and relentless labour. However, in contrast to the "finer" characters of the novel, Stephen, although he has to put up with so many difficulties in his life, strives to remain an honest and compassionate individual.
Note how he is described as a character who has had more than his fair share of suffering:
It is said that every life has its roses and thorns; there seemed, however, to have been a misadventure or mistake in Stephen's case, whereby somebody else had become possessed of his roses, and he had become possessed of the same somebody else's thorns in addition to his own. He had known, to use his words, a peck of trouble.
Clearly this is a character Dickens wants us to feel sympathy for, and his wider function in the play is to show the reality of industrialisation as experienced through the working class - the day to day workers who have to struggle to survive in a world where the Bounderby's exploit them at every turn.