Schaalman is like the Voldemort of this world, except instead of He-Who-Shall-Not-Be-Named, he's He-With-Too-Many-Names. When we first see him, he is Yehudah Schaalman. He makes the Golem, and it's a little sketchy (we do not want to know where he got her eyes and hair). And then we don't see him for a while…
But boy, does he come back into the story. We get his background, in which we find out that he left the Rabbinate for evil. He never really fit in, being shunned in Europe by both Prussians and Poles, and "his entire life was a catalog of misdeeds. Sins of pride and laziness, or anger, arrogance, lust" (4.69), in search of "the secret of unending life" (10.4). What a long, diabolical trip it's been.
His search leads him to New York, where he is renamed Joseph Schall on Ellis Island. He ingratiates himself into Michael Levy's Sheltering House so that he has a place to stay. Eventually a magic spell leads him to the Golem, his golem, whom he sees as "a hunk of clay with teeth and hair" (18.8), kind of like a tetratoma tumor (no, we are not linking to an image of this—if you want to see it, that's between you and Google). It turns out he's really looking for the Jinni, who is the creature he captured years ago. When they connect, both their memories come back.
Schaalman was Wahab ibn Malik a thousand years ago, and he already knew the secret to eternal life. Kind of, anyway. He's been born and reborn over and over across a thousand years, and as long as the Jinni is alive, he will continue to do so. Wee.
Ibn Malik is pretty much your classic villain, driven by selfishness and evil and not much else. However, there is a little irony to his tale because, as Schall, he ends up helping so many people in need at the Sheltering House. Michael even points this out to Schaalman (right before Schaalman kills him) saying, "In fact, if you think about it, all those men, the ones you hated helping—they've all moved on from here, to bigger and better things. You're the one who's been left behind" (27.130). This proves that if bad guys would put all the evil genius to good use, the world might have a lot fewer problems.