In Great Expectations, who is Orlick, and what is his importance in the novel?

Orlick is a rather frightening character who helps Joe out at the forge; he is, like Pip, an apprentice in-training to become a blacksmith.  At first, he just seems like kind-of a mean, scary guy that hangs around the forge quite a bit, and goes and gets slightly drunk at the local tavern every evening.  But, as the story progresses, he ends up playing quite a significant role in some key events.  First of all, Pip suspects him to be the one that irreversibly harms his sister.  He comes home one day to find his sister hurt badly, and after that, she can barely speak or move.  No one really knows what happens, but Orlick was suspiciously unaccounted for during the events, and his sister seems very animated whenever he comes around after that.

Later on in the story, Pip runs into Orlick again, and the nasty character threatens harm and murder.  He traps Pip in an old shack in the middle of nowhere, and has full intentions of murdering him.  So, overall, Orlick is a villian, one that Dickens uses to cause great harm and suspense in the story from beginning to end.  I hope that those thoughts helped; good luck!