The New York City-based character actor had numerous roles on shows ranging from Succession to Law & Order. But his most recent memorable role was on the first season of You as book store owner Mr. Mooney, a surrogate father to Joe Goldberg. "Mark Blum was beloved by actors, writers, theater folk, tv and movie people," tweeted Law & Order: SVU showrunner Warren Leight. "As a New York stalwart, he of course appeared on L&O, SVU, and Crim Intent. I was lucky to work with him several times, and luckier to know him. Sending love to all who mourn his loss."