Željko Ivanek (/ˈʒɛlkoʊ ɪˈvɑːnɪk/; Slovene: [ˈʒɛːlkɔ iˈʋaːnək]; born August 15, 1957) is a Slovenian-American actor. His accolades include an Actor Award, a Drama Desk Award, and a Primetime Emmy Award, as well as nominations for three Tony Awards.

Ivanek's film credits include Courage Under Fire (1996), Donnie Brasco (1997), Hannibal, Black Hawk Down (both 2001), Unfaithful (2002), The Manchurian Candidate (2004), Live Free or Die Hard (2007), The Bourne Legacy, Argo, Seven Psychopaths (all 2012). He has appeared in several films by Lars von Trier, including Dancer in the Dark (2000), Dogville (2003), and Manderlay (2005). In 2017, he appeared in Three Billboards Outside Ebbing, Missouri, receiving a Screen Actors Guild Award for his performance.

Ivanek portrayed Ray Fiske on the FX television series Damages (2007–2010), for which he won the 2008 Primetime Emmy for Outstanding Supporting Actor. He also appeared as Ed Danvers on Homicide: Life on the Street (1993–1999) and Russell Jackson on the CBS drama Madam Secretary (2014–2019), and has had recurring roles on series such as Oz (1997–2003), 24 (2002), True Blood (2008), Heroes (2009), Big Love (2009–2010), Banshee (2014), and 12 Monkeys (2015–2017). Since 2023, he has starred as "The Croat" on AMC's The Walking Dead: Dead City.

Ivanek was born in Ljubljana, PR Slovenia, FPR Yugoslavia. His father was Ferdo Ivanek, who grew up in Zajezda, in the Croatian region of Hrvatsko Zagorje, and spent his later childhood in Varaždin. In 1960, Željko, his younger brother Ivan, and his mother immigrated to Palo Alto, California, where his father was working as a research assistant at the Department of Electrical Engineering at Stanford University. His mother also worked at Stanford University as a project manager.

In 1962, Ivanek and his family moved back to Slovenia for five years; they returned to Palo Alto in 1967. Having performed in numerous community theater plays in the San Francisco Bay Area, Ivanek graduated from Ellwood P. Cubberley High School in Palo Alto in 1975. In 1978, Ivanek graduated from Yale University, majoring in theater. He later attended the London Academy of Music and Dramatic Art.

Ivanek has worked extensively on the stage. In 1982, he originated the role of Hally in Athol Fugard's play "Master Harold"...and the Boys. He appeared in the U.S. premieres of Cloud Nine (for which he earned the 1981 Drama Desk Award for Outstanding Featured Actor in a Play), and The Pillowman. He performs frequently on Broadway and has been nominated for three Tony Awards for his performances in the original production of Brighton Beach Memoirs, in Two Shakespearean Actors, and in a revival of The Caine Mutiny Court-Martial, alongside David Schwimmer and Tim Daly.

However, Ivanek is perhaps best known for his supporting roles in a number of well-known television series. His first television role was as Sammie Wheaton on the soap opera The Edge of Night. Other roles include Emile Danko in Heroes; Roland in The X-Files; prosecuting attorney Ed Danvers in Homicide: Life on the Street; Ray Fiske in Damages (for which received the Primetime Emmy Award for Outstanding Supporting Actor in a Drama Series); J.J. in Big Love; the Magister in True Blood; Governor James Devlin in Oz; Serbian terrorist Andre Drazen in 24; and Blake Sterling, the Director of National Intelligence in the NBC drama series The Event.

Ivanek played Russell Jackson in the TV series Madam Secretary. He portrayed John Dickinson, the Pennsylvania representative to the Second Continental Congress, in the miniseries John Adams. He has guest-starred on such shows as Law & Order: Special Victims Unit and House. He has appeared several times on Law & Order, both as one-off characters and as Ed Danvers in crossover episodes with Homicide: Life on the Street.