Pip meets many unknown characters during the course of this chapter and the one preceding it. This particular gentleman on the stair scares Pip because of his large stature. Pip describes him as
a burly man of exceedingly dark complexion.
This man evaluated Pip immediately as if he was a professional at sizing up young boys. The man encourages Pip to behave.
Pip further describes the man as having eyes set back into his head, being prematurely bald, having bushy eyebrows, and having a 5 'o clock shadow ready to appear in his beard. He thought this man was suspicious and "disagreeably sharp."
Pip never at this point learns of this man's identity, and the man just goes away.