On television, he is noted as a recurring cast member on Boardwalk Empire who portrayed real-life bootlegger George Remus, for appearing on Billions, and as Errol Childress in the first season of the crime drama True Detective.
1998
Fleshler's first major film was 1998's A Price Above Rubies.
More recently, he has appeared in such films as Blue Jasmine, Joker,
A Most Violent Year, God's Pocket, and The Rendezvous.
Fleshler's television credits include Billions, Barry, Sex and the City, Law & Order, Law & Order: Special Victims Unit, Fringe, Third Watch, Bored to Death, The Good Wife, FBI: Most Wanted, The Following.
He portrayed George Remus in seasons 2–4 of Boardwalk Empire, and Errol Childress in Season 1 of True Detective.
He played Dr. Cordell Doemling, Mason Verger's physician and henchman, in season 3 of Hannibal.
He played Judge Roth in the miniseries The Night Of.
2018
He also starred as Chechen mob boss, Goran Pazar in the HBO black comedy series Barry (2018-2022).
2019
He had a supporting role in the 2019 film Joker.
Fleshler was born to a Jewish family and studied acting at New York University's Tisch School of the Performing Arts, from which he has an MFA.
He was also cast as Officer Christopher Lasky in episode 3 of the 2019 revival of The Twilight Zone.
Fleshler's Broadway credits include Death of a Salesman, Guys and Dolls, Arcadia, and The Merchant of Venice.
Off-Broadway, he has appeared in such plays as Measure for Measure and Pericles, Prince of Tyre.