He has published profiles and personal essays in The New Yorker, Esquire, GQ, The Washington Post, New York, and Slate.
[1] He graduated magna cum laude from Brown University, where he was elected to Phi Beta Kappa and won the American Historical Society Prize for his senior thesis.
[6] Rolling Stone reprinted a chapter upon publication, praising Karlen, the musician's "longtime confidant" for telling “the story not just of Prince's life, but of a rare decades long friendship between a writer and an iconic artist";[7] The Star Tribune, the musician's hometown paper, called Karlen's work "easily the most telling book about the late Prince.
"[8] Karlen's other books, including several national bestsellers, vary in topic ranging from vaudeville ("Take My Life, Please"); religious assimilation ("Shanda"); minor league baseball ("Slouching Toward Fargo"); the intersection between politics and organized crime ("Augie’s Secrets") and linguistics ("The Story of Yiddish").
In September 2023 he was featured prominently in the Netflix film The Saint of Second Chances directed by Academy Award winning documentarian Morgan Neville ("20 Feet From Stardom") and Jeff Malmberg.