William Patterson Alexander (July 25, 1805 – August 13, 1884) was an American Presbyterian missionary born in Paris, Kentucky, who dedicated much of his life to Christian mission work in the Kingdom of Hawaii after arriving there with the fifth company of the American Board of Commissioners for Foreign Missions in 1832. He served at mission stations including Waioli on Kauai and later became principal of Lahainaluna School, contributing to both religious outreach and education in the islands and helping unite Presbyterian and Congregational churches into the Hawaiian Evangelical Association. Alexander continued mission work and church support in Hawaii until 1882, and after retirement he died in Oakland, California, where he was buried in Mountain View Cemetery.