In order to better combat reactionaries.
Being called Mr. Wu is actually because of one of his pen names.
Origin of pen name:
19 19 In September, the Tianjin Students' Federation and the Tianjin Women's Patriotic Association, which were organized by Tianjin female students, formed the Enlightenment Society, and published the occasional publication Awakening, requiring all leading members to write articles under pseudonyms. Considering the expansion of the organization in the future, they compiled 50 numbers, and the members drew lots to decide which number. Zhou Enlai grabbed No.5, and in order to sound like a China name, he took a pen name according to the homophonic sound of No.5.. Zhou Enlai called it "Wu Hao".
Revolutionaries are sometimes caught if they can't directly reveal their true identity by writing articles.