It might as well be the thing that scares you the most".[5] Phoenix lost 52 pounds (24 kg) in preparation,[6][9] and based his laugh on "videos of people suffering from pathological laughter".[10] He also sought to portray a character that audiences could not identify with and did not look to previous Joker actors for inspiration; instead, he read a book about political assassinations so he could understand killers and motivations.[5] Robert De Niro as Murray Franklin:[11] A talk show host who plays a role in Arthur's downfall.[10] De Niro said his role in Joker pays homage to his character from The King of Comedy (1983), Rupert Pupkin, who is a comedian obsessed with a talk-show host.[11] Zazie Beetz as Sophie Dumond:[13] A cynical single mother and Arthur's love interest.[13][12] Beetz, a "huge fan" of Phoenix, said that it was "an honor" to work with him,[15] and that she learned a lot working with him on set.[16] Frances Conroy as Penny Fleck: Arthur's mother.[15]