(written from a Production point of view)
Kassir first acquired fame in 1984, when he bested Sinbad in the stand-up comedy talent competition on Ed McMahon's Star Search. Today, he is perhaps best recognized as the voice of the cackling, maniacal Crypt Keeper on the HBO horror anthology series Tales from the Crypt and its subsequent movie spin-offs. As The Crypt Keeper, Kassir provided a pun-filled opening and closing narrative for each episode, similar to Alfred Hitchcock or The Twilight Zone host Rod Serling. Kassir reprised his role as the Crypt Keeper for the feature films Tales From the Crypt: Demon Knight (with Brenda Bakke, Tim DeZarn, John Larroquette, Dick Miller, William Sadler, and John Schuck) and Tales From the Crypt: Bordello of Blood. Sadler appeared alongside the Crypt Keeper in the prologues of both Bordello of Blood and an episode of the series, playing a mummy and the Grim Reaper, respectively.
Kassir is also known for his role as Bulgarian football player Zagreb Shkenusky on another HBO series, 1st & Ten, which aired from 1984 through 1990.
Although he became primarily a voice actor following the end of 1st & Ten, he made occasional live-action appearances on television. Besides his role on Voyager, he has also been seen on The Facts of Life, Tour of Duty (along with fellow Star Trek guest stars Dan Gauthier, Robert Ito, and Patrick Kilpatrick), Dream On (starring Michael McKean and Paul Dooley), The Single Guy (with Mark Moses and Olivia d'Abo), Malcolm & Eddie (with Tucker Smallwood), Sliders, and Friends, and more recently in Philly (starring Ron Canada), CSI, Joan of Arcadia, Cold Case, CSI: Miami, Charmed, and Bones. He was also a regular performer on the hit Nickelodeon sketch comedy series The Amanda Show.
In 1997, Kassir played The Atom (and his alter ego, Ray Palmer) in the made-for-TV adaptation of DC Comics' Justice League of America, which co-starred David Ogden Stiers and Miguel Ferrer. In 2000, Kassir proved he had a knack for drama as well as comedy with his portrayal of Shemp Howard in the telefilm The Three Stooges. Kassir's other TV movie credits include 1996's Encino Woman (co-starring Clarence Williams III).
Kassir has also appeared in a few live-action feature films. These include 1995's Monster Mash: The Movie and CyberTracker II (the latter also featuring Anthony De Longis, Stephen Rowe, Stacie Foster and Athena Massey), and the 1996 comedy spoof Spy Hard (with Michael Berryman, Bruce Gray, and the Klimazsewski twins Diane and Elaine). In 2002, Kassir co-starred with Star Trek: Deep Space Nine star Armin Shimerman in a short film called Who Slew Simon Thaddeus Mulberry Pew, with Kassir playing the title role. Kassir also starred in 2005's Reefer Madness: The Movie Musical with Steven Weber.
As a voice actor, he was worked on such series as Eek! The Cat, Tiny Toon Adventures, The Wild Thornberrys, CatDog, The Simpsons, Buzz Lightyear of Star Command, and Samurai Jack. He also voiced Meeko the raccoon in the 1995 Disney animated film Pocahontas and its 1998 direct-to-video sequel Pocahontas II: Journey to a New World.