Given the following context:

Arising form a moribund aviation company, in the 1970s, the new Canadair Challenger business jet on the drawing board was a risky proposition. Derived from a design by American inventor and aircraft developer Bill Lear, Canadair Chief Designer Harry Halton married a wide-body fuselage with a high performance ("supercritical") wing and state-of-the-art engines. With banks and the then federal Minister of Industry, Trade and Commerce Jean Chrétien requiring 50 "firm orders", a Canadair sales team was dispatched to sell a "paper aircraft" with only sales brochures, scale models and a wooden mock-up to go on. The innovative Challenger design boasted industry-leading performance. It promised to be faster, cheaper to fly, and more comfortable than any other business jet.
With orders of 56 aircraft from North America, Europe and the Middle East, Canadair's top management, headed by Frederick Kearns, gave a "go" to the Challenger project. As the first prototype was completed, competitors touted their "off-the shelf" availability. Although months late, the Challenger was finally unveiled and prepared for its maiden flight, piloted by Canadair Chief Test Pilot Doug Adkins. After successful tests at the company plant in Montreal, the Challenger was flown to Mojave, California, to complete its arduous flight testing in order to obtain its certification for worldwide operation.

answer the following question:

Who added to the American inventor's design for the Challenger? 

Harry Halton