In 1949, Russell Baker and John McKenzie started a four-lawyer firm in Chicago. Six decades later, the firm bearing those two names has 4,215 lawyers across 76 offices in 47 countries. It is the world’s largest firm when measured by lawyers, revenue or markets. “It was built on one man’s international vision,” said Michael S. Smith, referring to Baker. In July, Smith became managing partner of the 215-lawyer Chicago office of Baker & McKenzie LLP. It’s the firm’s largest …