Context: William Hale Thompson (May 14, 1869 -- March 19, 1944) was an American politician, mayor of Chicago for three terms, from 1915 to 1923 and again from 1927 to 1931. Known as "Big Bill" Thompson, he is the last Republican to have served as mayor of Chicago to date. Historians rank Thompson among the most unethical mayors in American history, mainly for his open alliance with Al Capone. However, others recognize the effectiveness of his political methods and publicity-oriented campaigning, acknowledging him as a "Political Chameleon" and an effective political machine. TIME magazine said in 1931, "chief credit for creating 20th Century Politics Chicago Style" should go to William Thompson.

Question: who was the last republican mayor in chicago?
Steam of consciousness below:
The relevant sentence in the passage is: Known as "Big Bill" Thompson, he is the last Republican to have served as mayor of Chicago to date.
So, the answer is William Hale Thompson.