Question: who does the voice of justine in why him
Answer: and Zoey Deutch as Stephanie Fleming , Laird 's girlfriend , Ned and Barb 's daughter , and Scotty 's older sister Megan Mullally as Barb Fleming , Ned 's wife and Stephanie 's mother Cedric the Entertainer as Lou Dunne , Ned 's best friend and business partner Griffin Gluck as Scotty Fleming , Stephanie 's 15 - year old younger brother and Ned and Barb 's son Keegan - Michael Key as Gustav , Laird 's best friend , butler , calmer assistant and trainer , the billionaire 's European - hailing estate manager Kaley Cuoco as the voice of Justine , Laird 's in - home artificial intelligence Zack Pearlman as Kevin Dingle , Ned 's I.