Isadore Elliot Handler cofounded Mattel, Inc. which was named after Handler and his business partner Harold Matson. His wife, Ruth Mosko Handler, took over Matson's role when the Handlers bought out his share in the late 1940s.

Handler had a direct hand in the production of two Mattel product lines, Liddle Kiddles and Hot Wheels. Kiddles, introduced in 1966, were a great success and continued to be produced in different versions until the early 1970s. Hot Wheels was introduced in 1968 and is still in production today.