Joe is the husband of Pip's much older sister. He is a blacksmith, a humble occupation, somewhat like being a car mechanic today. When Pip's parents die it is the kind-hearted Joe, rather than Pip's sister, Mrs. Joe, who wants to take in Pip. From the start, the two males develop a special relationship in order to cope with the harsh, demanding Mrs. Joe.
Joe is especially good to the young Pip, who receives little kindness as a poor relation who is never expected to be more than a working class blacksmith in the village. Pip loves Joe dearly, as a neglected child would someone who paid special attention to him and treated him with gentleness.
When Pip finds out he is going to be made a gentleman, however, the relationship changes. As Pip moves to London, studies law, and wears the clothes and develops the manners of a gentleman, he becomes a snob. Now, he is ashamed of Joe: his work, his clothes, his manners, his speech. He even avoids seeing his oldest friend.
At the end of the novel, however, after Magwitch dies and Joe pays Pip's debts, Pip is humbled and transformed. He realizes once again the great worth of Joe (and Biddy, his new wife) and fully comes to understand that Joe is a true gentleman—because Pip now recognizes that character is more important than clothing or speech.