Who is Orlick and what does Pip think he did?

Pip is given clues about how Mrs. Joe became injured. We
do find it was Orlick, but Pip thinks it was him for about 30 chapters before it is
verified.

One day while Biddy and Pip are talking, Biddy
remembers some of the things that Mrs. Joe has tried to communicate. Mrs. Joe kept
writing this character on her board that looked like a t or a J. Thinking that the J had
something to do with Joe, the idea of Orlick was regularly dismissed. But when Biddy and
Pip put together that the t or J might have been a hammer, everything begins to make
sense. The hammer represents Orlick because that's what he does as a
blacksmith.