Answer:
The magician
Step-by-step explanation
The magician remembers Aladdin perishing in the cave, and also all these riches. This magician character would have not known that IF unless he'd been there or done that.
Also, in the excerpt, it explains, "...he was determined to get a hold of the lamp, and again plunge Aladdin into the deepest poverty. We know that because of this sentence, we can tell he is not a good guy, and has bad plans on Aladdin. An antagonist is a person who is an enemy, foe, or opponent.
The magician is the antagonist.
Hope this helped.