At Disney Klein worked as an animator and storyman. He worked on shorts such as Mother Goose Goes Hollywood and Lonsesome Ghosts just to name a few.
He left Disney in 1939 to work for Mintz and then later Paul Terry. He penned the cartoon Might Mouse. In the late 40's he went to work for Paramaount to work on Casper, Little Audrey, Little Lulu, and Popeye. He retired from animation in the 1960's. Klein is credited as I. Klein, Izzy Dlein, and I. Klien. He died in 1986.