Affiliated Managers Group and Parnassus Investments — the largest U.S. asset manager focused purely on environmental, social, and governance — have been talking about a potential deal for 10 years. This month the two reached an agreement. AMG has taken a majority stake in Parnassus, which has $47 billion in assets and is one of the longest running U.S. firms in ESG. The active manager was founded in San Francisco in 1984. More than 95 percent of its mutual fund assets are in strategies with a Morningstar Rating of 4 or 5 stars. Once the deal closes, Parnassus will remain independent and employees will have more equity in the firm.