William Julius Mann (1819–1892) was an American Lutheran theologian and author, born in Stuttgart, Germany.
Three years later he was invited by his friend Dr. Philip Schaff to come to the United States and settled in Philadelphia.
From its establishment in 1864 almost to his death he was professor of symbolics (the study of the lutheran confessions) at the Lutheran Theological Seminary.
With Dr. Schaff he edited Der deutsche Kirchenfreund.
His daughter, Emma T. Mann, wrote his Life, (Philadelphia, 1893).