Zinn, most famous for A People's History of the United States: 1492-Present, wrote history from the point of view of the people who weren't Washington and Jefferson, but who had to live with the consequences of the policies of such great men. He wrote America's history from the point of view of native Americans, women, immigrants (of the non-Pilgrim variety), working people, farm workers, and factory laborers.
If you ever wanted to know why there's a fortress-like armory a couple of blocks north from NW 10th and Burnside in Portland (not far from where Powell's Books sell's Zinn's books), the history books you had in school didn't tell you. And the books approved by the Texas State Board of Education absolutely won't tell you. But Howard Zinn's "People's History"--it'll tell you.
No wonder his job security was constantly under attack, however unsuccessfully. It's a miracle that the president of Boston University only accused him once (falsely) of arson. That was in the polite days. Today, they'd chase him up a tree and set fire to it. (Or they'd send some conservative bloggers try to break into his office and tap his phones.)
Zinn was also Alice Walker's history professor at Spelman College.
This isn't a bad epitaph for anyone; it's perfect for Howard Zinn:
On his last day at BU, Dr. Zinn ended class 30 minutes early so he could join a picket line and urged the 500 students attending his lecture to come along. A hundred did so.