Question About Chapter 27

In chapter 27 of Great Expectations, Pip talks about the Avenger.

I had got on so fast of late that I had even started a boy in boots- top boots- in bondage and slavery to whom I might be said to pass my days. For, after I had made this monster (out of the refuse of my washerwoman's family) and had clothed him with a blue coat, canary waistcoat, white cravat, creamy breeches, and the boots already mentioned, I had to find him a little to do and a great deal to eat; and with both of these horrible requirements he haunted my existence. (233)

I understand that this was discussed in class on Monday, but since I wasn't there, I have no idea what it is talking about. It mentions how it is a slave to him and how he has clothed it. Could someone please explain to me who exactly the Avenger is and why it is mentioned in context with Joe's visit to Pip in London.