Dec. 17, 2020 9:51 am ET As corporate executives in the late 1970s grew baffled by a proliferation of computer and other information-technology choices, Gideon Gartner saw an opportunity: Why not offer them advice on what to buy, when to buy it and how much to pay? Mr. Gartner, a former International Business Machines Corp. executive and star Wall Street analyst, in 1979 formed Gartner Group, now known as Gartner Inc . , to sell that advice in the form of punchy two-page notes, client consultations and eventually mammoth conferences. He hired aggressive sales people and analysts, paid them well and created a durable business, now part of the S&P 500, with revenue of $4.2 billion last year and a current stock market value of about $14 billion.