William Cowper Alexander (May 20, 1806 – August 23, 1874) was an American lawyer, politician, and insurance executive. He served as President of the New Jersey State Senate and as President of the Equitable Life Assurance Society.
Alexander was born in 1806 in Prince Edward County, Virginia, the second son of noted Presbyterian theologian Archibald Alexander and his wife Janetta Waddel. His elder brother James Waddel Alexander (1804–1859) would also become a Presbyterian theologian and minister. Another brother, Joseph Addison Alexander (1809–1860), would become a biblical scholar.
Alexander's father was president of Hampden-Sydney College in Virginia before being called to serve as minister of the Third Presbyterian Church in Philadelphia in 1807. The family then moved to Princeton, New Jersey when Archibald Alexander was named the first professor of the Princeton Theological Seminary in 1812.
Alexander graduated from the College of New Jersey (now Princeton University) in 1824 and was admitted to the bar of New Jersey as an attorney in 1828. He opened an office in Princeton and attended to his professional business there for about thirty years. He also joined the militia company known as the Princeton Blues and achieved the rank of colonel.
Alexander never obtained his license as counsellor and took a greater interest in politics than law. He entered the New Jersey General Assembly in 1836 as a Democrat from Middlesex County (before the formation of Mercer County). In 1851 he succeeded Charles Smith Olden as a member of the New Jersey Senate from Mercer County, serving as president of that body for four terms.