Great Expectations Question 2

One character in this weeks reading that I don't fully understand is Compeyson. Abel Magwitch tells a story about him on page 346 which confused me a bit. Magwitch says, "A man whose skull I'd crack wi' this poker, like a claw of lobster, if i'd got it on this hob." Obviously magwitch doesn't like this man. What I wanna know is; Who is Compeyson? My guess is that Compeyson is the other convict.