In 1986, Michael Dell brought in Lee Walker, a 51-year-old venture capitalist, as president and chief operating officer, to serve as Michael's mentor and implement Michael's ideas for growing the company. Walker was also instrumental in recruiting members to the board of directors when the company went public in 1988. Walker retired in 1990 due to health, and Michael Dell hired Morton Meyerson, former CEO and president of Electronic Data Systems to transform the company from a fast-growing medium-sized firm into a billion-dollar enterprise.

What year did Michael Dell bring in Lee Walker to the company?