I think the most important thing we should know and remember about Howard Zinn is that he was a social activist, always speaking his mind whether people were going to like what he said or not.
Zinn was born in Brooklyn, NY to an immigrant working class Jewish family. His mother and father had come over before WWI broke out, they both worked in factories and weren't very educated. Despite this, they gave Zinn books as a child, and he ended up going to Thomas Jefferson High School and studying creative writing in a special program. After high school, Zinn wanted to fight fascism so he joined the Air Force for WWII. He became a bombardier, and was involved in the bombings of several places in Europe during the war. He was also one of the first bombers to use napalm, which had devastating results. He eventually returned to some of the places he had bombed to interview the survivors about the horrors of war, and their recollections turned Zinn away from war. He found out that he was responsible for the killing of hundreds of civilians and retreating soldiers, right before the end of the war. The US government's recounts of these same events told a different story entirely.
After the war, Zinn attended New York University and obtained his B.A. He went on to Columbia University and got his Master's and a PhD in History with a minor in political science. He became a professor at Spelman University and later at Boston University. He was an outspoken advocate of the Civil Rights movement. He believed that the United States was publishing textbooks that had very limited points of view, so he published his own which went on to be very influential. He mentored Alice Walker, who went on the write The Color Purple. He criticized the Kennedy administration and the FBI for not responding effectively to all the injustices occurring in Georgia.
He supported socialism, a radical idea to most at the time and even still today. He was quoted saying he would describe himself as "something of an anarchist, something of a socialist. Maybe a democratic socialist." The FBI pegged him as a Communist supporter because of his ideas concerning socialism.
He died in 2010, but his legacy will live on for all of history.