According to Us Weekly, Beanie’s given moniker is Elizabeth Greer Feldstein. As the actress recalled, a childhood nanny nicknamed her “Elizabeanie,” and the second half of the silly pet name stuck. “Since I was like, 2 years old, it was just exclusively Beanie,” she told 2015 profile The Wesleyan Argus in 2015, adding that Jonah was a particular fan of doing away with Elizabeth altogether when they were just kids.

Source: https://www.distractify.com/p/why-did-jonah-hill-change-his-name