Jeff Widener, 1989. Unknown Beijing protester blocking a column of T-59 tanks the day after the Tiananmen Square massacre.
From Wikipedia
Tank Man is an unidentified individual, presumed to be a Chinese man, who stood in front of a column of Type 59 tanks on Chang'an Avenue near Tiananmen Square in Beijing on June 5, 1989. The confrontation occurred one day after the government of China forcibly cleared the square following six weeks of pro-democracy demonstrations, resulting in the deaths of hundreds of people, primarily in areas surrounding the square.