Who is old joe and what is his purpose?

Old Joe is a pawn broker. The charwoman, the laundress, and the undertaker each visited Old Joe in order to sell the goods the stole from Scrooge's home after he died (one of the visions). Old Joe's character and greediness mirror Scrooge..... he sees that his own life could be one and the same as the broker's.

“Spirit!” said Scrooge, shuddering from head to foot. “I see, I see. The case of this unhappy man might be my own. My life tends that way, now. Merciful Heaven, what is this!”

joe mama