His most famous song is arguably "Cruella de Vil" from the 1961 Disney animated feature One Hundred and One Dalmatians. That same year, he also wrote the story and new lyrics to sixteen tunes for the film Babes in Toyland. In later years, he wrote songs, stories, and did voice-over work for the PBS children's series Big Blue Marble, and well as working on a number of projects for television commercials. He also composed "When The Buzzards Return To Hinckley Ridge" for the 1969 Disney animated short, "It's Tough to Be a Bird", which went on to win the Academy Award for Best Short Subject in 1970. The song was sung by comedienne Ruth Buzzi.

Leven was also the original voice of Snoopy, and was in Snap, Crackle, Pop commercials. He also wrote the Little Ranger Nature series for Disney in the 1960s.

His work has been honored with two Emmy Awards and two Peabody Awards.

A conservationist and talented fly fisherman, in retirement Leven traveled the world in pursuit of fish and became a beloved fixture along Northern California rivers in particular.[1] He features prominently in the 2009 documentary Rivers of a Lost Coast, on the decline of the California steelhead population. -Wikipedia