William Irwin was an American politician from the Democratic Party who served as the 13th governor of California between 1875 and 1880. He previously served as acting lieutenant governor for nine months in 1875.

The president pro tempore of the California State Senate is the highest-ranking leader and most powerful member of the California State Senate. The officeholder also chairs the Senate Rules Committee. At the beginning of each two-year session, all members of the body elect a new State Senate President pro tempore. The President pro tempore is chosen by the other Senators.