Task: Question Answering
Input (English): Passage: Richard Gaddis is a small-time crook with a penchant for con games. To hook marks, he acts like a well-to-do businessman, dressing like one and driving a Mercedes-Benz S500, believing that one must look like a professional in order to be a successful conman.
Gaddis is searching for a new partner with whom he can perform more sophisticated cons.  He discovers Rodrigo after he sees the young man playing some minor con games in a casino-bar.  When Rodrigo is caught, Gaddis acts the part of a vice officer to save him from being arrested.  Rodrigo's contribution is a face and naive manner so trustable that he is able to con anyone, while Richard is both completely unprincipled and clever.  After several small tests to determine Rodrigo's trustworthiness, he suggests a partnership, to which Rodrigo quickly agrees.
Although Rodrigo distrusts Richard greatly, he agrees to partner him on a gigantic scam, provided he gets a percentage of the money gained to help his ailing father, who is in trouble because of his gambling debts.   Richard accepts, and they plan to sell a fraudulent version of a silver certificate currency note to William Hannigan, a rich collector who is in town.
Gyllenhaal plays Gaddis' sister Valerie, a concierge at a hotel.  When Hannigan takes a fancy to the uptight but very sexy Valerie, Gaddis is forced to pull her into the scam, the price of which is Richard's admission to their brother Michael that he has cheated him out of his share of their inheritance. The plot twists constantly as each of the characters becomes more deeply invested in the scam, and the ever-deceitful Richard tries to cheat Rodrigo, Valerie and Michael out of their share of the take.
In the twist ending, it is revealed that all the major players involved, including Rodrigo and Hannigan, were playing a confidence game against Gaddis from the very beginning, so that Valerie and Michael could rightfully take their share of their inheritance. 
Question: What is the last name of the person that is interested in the sister of the small-time crook?
Output (English): Hannigan.