According to Melvin L. Katten, founding partner of Katten Muchin Rosenman LLP, building one of the biggest law firms in the country required the “hard work and unswerving determination of a few entrepreneurial lawyers” — and also a bit of luck.Nearly 47 years after co-founding the firm that bears his name, Katten retired this month.Founded in 1974 as Katten Muchin Zavis, the firm started as a boutique tax firm with 24 attorneys. Today, it’s the sixth-largest law office in Chicago, counting 270 lawyers in Chicago Lawyer’s …