His second son, William Cowper Alexander (1806–1874) served as president of the New Jersey State Senate and as the first president of the Equitable Life Assurance Society.
His younger brothers included William Cowper Alexander (1806-1874), president of the New Jersey State Senate and first president of the Equitable Life Assurance Society, and Joseph Addison Alexander (1809-1860), a biblical scholar.
Shortly after leaving the University of Virginia, Alexander was offered a temporary position with The Equitable Life Assurance Society of the United States, where his uncle, William Cowper Alexander, had served as first president.
His brother, Presbyterian minister James Waddel Alexander, had become the patron of Equitable founder Henry Baldwin Hyde, and many of the company's original directors were members of Rev. Alexander's Fifth Avenue Presbyterian Church.
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