Who started the protests that led to the May Fourth Movement?

The May Fourth Movement (Chinese: 五四运动; pinyin: Wǔsì Yùndòng) was an anti-imperialist, cultural, and political movement growing out of student participants in Beijing on 4 May 1919, protesting against the Chinese government's weak response to the Treaty of Versailles, especially allowing Japan to receive territories in ...

I am pretty sure this is the answer

Student protests in Beijing on 4 May 1919 led to the May Fourth Movement.

Students protested against the Chinese government's weak raction to the Treaty of Versailles, particularly allowing Japan to retain territories in Shandong that had been surrendered by Germany after the Siege of Tsingtao in 1914.

The term "May Fourth Movement" generally refers to the period during 1915-1921 more often refered to as the New Culture Movement.