He first rose to prominence in the 1950s as the Native American Cochise on Broken Arrow. He also played Apache Marshal Sam Buckhart in Law of the Plainsman, a spin-off of The Rifleman. During filming, 20th Century Fox set up a date between him and actress Barbara Eden, who would eventually play Jeannie on I Dream of Jeannie. The two eventually got married and had a son together.
Among sci-fi fans, he's famous for playing the Klingon captain Kang in the Star Trek: The Original Series episode "Day of the Dove", a role he would reprise decades later on Star Trek: Deep Space Nine and Star Trek: Voyager.
But it was his portrayal of Mr. Freeze in the DCAU which would garner him the greatest acclaim of all. Starting in the Batman: The Animated Series episode "Heart of Ice", he changed Freeze from a silly and unremarkable one-shot villain from the Silver Age into a tragic Anti-Villain.
He passed away in July 2013 at age 91.
- Dragnet - "The Big Rod" in the 1950s TV series
- Broken Arrow (1956 TV series)
- Alfred Hitchcock Presents - "The Orderly World of Mr. Appleby", "The Baby Sitter", "Shopping for Death"
- The Rifleman - "The Indian", "The Raid"
- Voyage to the Bottom of the Sea - the original 1961 film
- Voyage to the Bottom of the Sea - the TV episode "Hot Line"
- The Untouchables - "Nicky", "The Jamaica Ginger Story"
- The Outer Limits (1963) - "Soldier"
- Kraft Suspense Theatre - "A Truce to Terror"
- I Dream of Jeannie - Acted in "Happy Anniversary", "The Battle of Waikiki", and "My Sister, the Homewrecker"; directed "One Jeannie Beats Four of a Kind"
- Lost in Space - "The Challenge"
- The Time Tunnel - "The Kidnappers"
- Land of the Giants - "On a Clear Night You Can See Earth"
- The Fugitive - "The Savage Street"
- Star Trek: The Original Series - "Day of the Dove"
- The Streets of San Francisco - "The Year of the Locusts"
- Hawaii Five-O - "Death Is a Company Policy"
- Mission: Impossible - "The Western"
- The Rockford Files - "Joey Blue Eyes"
- Kojak - "Justice Deferred"
- Buck Rogers in the 25th Century - Kane during the 1979-80 season
- Reading Rainbow - Narrated two books
- Rambo: The Force of Freedom (as the series' Big Bad, General Warhawk)
- Batman: The Animated Series - "Heart of Ice", "Deep Freeze", "Cold Comfort"
- Star Trek: Deep Space Nine - "Blood Oath"
- Star Trek: Voyager - "Flashback"
- Murder, She Wrote - "The Last Flight of the Dixie Damsel"
- Babylon 5 - "The Geometry of Shadows"
- Batman & Mr. Freeze: Sub-Zero
- Batman Beyond - "Meltdown"