WHEN BUY-OUT firms first came to prominence in the 1980s, they were seen as wolves in fine Italian wool. Private-equity (PE) companies won a reputation for devouring companies, which they loaded with debt, stripped of assets and rid of workers. All to make a killing for their millionaire investors—and themselves. In the past 30 years the industry has softened its image while maintaining a red-bloodedly capitalist devotion to returns. PE firms have diversified into a wider array of assets, from commercial property to corporate debt; anything not traded in public markets is fair game.