In 1948 he wrote music for the original Max Fleischer/Jam Handy animated adaptation of the Rudolph the Red-Nosed Reindeer story.
The producers elected to use the Johnny Marks version of the song, but Kleinsinger retained partial songwriting credit; the resulting royalties made him wealthy.
[6] Kleinsinger's version of the song was released by RCA on a 1964 LP sung by Paul Wing with Russ Case's orchestra.
This began with a 1954 concept record album Archy & Mehitabel starring Carol Channing, and included a 1954 opera premiered by the Little Orchestra Society, the 1957 Broadway musical Shinbone Alley (which ran for 49 performances featuring Eddie Bracken and Eartha Kitt), and the 1970 film adaptation Shinbone Alley.
[10] In addition to the numerous children's and programmatic compositions, Kleinsinger composed more traditional classical music, including a cello concerto and a quintet for clarinet and strings.
He gained notoriety for his hobby of recreating a tropical environment in the apartment, including keeping iguana, tarantulas, walking catfish, turtles, exotic birds, and a baby hippo.