Who was the man working as a shoemaker in the garret in A Tale of Two Cities?

The man in question is none other than Dr. Manette. Since being released from the Bastille, he's been working as a shoemaker in a garret owned by Monsieur Defarge. He also worked as a shoemaker while he was in prison; it was a way for Manette to keep himself occupied and to prevent himself from going out of his mind in such an unmitigated hellhole.
Nevertheless, this only worked up to a point. Manette has been still been deeply traumatized by his experiences of the Bastille. This is painfully obvious to his daughter, Lucie, when she meets up him again. Her father may be free, but he's a broken man; at first, he doesn't even recognize her. But Manette quickly identifies Lucie from her lovely golden locks.
Now that Dr. Manette and Lucie have been reunited at last, Lucie's determined to take good care of her father. This means getting out of France as soon as possible and heading off to England, where they will start a new life together.