Malcolm Stein is a dwarf who, together with his apprentice, runs the blacksmith shop in Little Mahakam, the non-human district of Vizima's Συνοικία του Ναού. He will serve only people who come recommended, and will not have his weapons be used against non-humans. So take heed, and do not cross Yaevinn or Malcolm's services will be off limits to you. Alternatively, Zoltan's word carries a lot of weight with both Malcolm and his apprentice.
His main competition in town is the Σιδεράς του Τάγματος, who has recently acquired some Mahakaman anvils remarkably similar to those confiscated by the City Guard from Malcolm's own smithy. But if things seem bleak in Chapter II, they are even bleaker in Chapter III where his workplace is pretty much reduced to a firepit.
In Chapter V, it seems Malcolm has relocated to the makeshift forge in Old Vizima to help the Scoia'tael cause. It is he who makes Raven's Armour for Γκέραλτ. Although he is not specifically identified, the conversation he has with Γκέραλτ would only make sense if it was Malcolm.
Incidentally the name Stein means stone in German.