Zhao ZiYang was the Secretary General of the Communist Party of China at the time of the Tianamen Square crisis. When the tanks and troops swept the students out of Tianamen Square on June 4, 1989, Zhao Ziyang was also swept from power.
Dead Chinese leaders have historically shown the remarkable tendency to come back to life and regain power. This only happens in China. That is the reason why everybody is reading and intensely studying the Zhao Ziyang letter, although nobody would study a letter written by Ronald Reagan, if he were to write one today.