Mary Esther Miller MacGregor, (August 27, 1872 – February 10, 1961) also known as Marian Keith, was a Canadian author of fiction. MacGregor was born in Rugby, Ontario in 1872. Her parents were John Miller, a schoolteacher, and Mary Brown Johnston. Both parents were of Scottish ancestry. She was the eldest of five children. She attended school in Edgar, Ontario, and the Orillia Collegiate Institute. She received her teacher's certificate from the Toronto Normal school in 1896. Beginning in 1899, she taught for seven years in Orillia. She began writing in 1905. She contributed a column to Teacher's Monthly and then worked on the editorial staff of the Presbyterian Church's Sunday School Publications. In 1906 when she tried to publish her first novel she learned that her name, "Esther Miller" was already in use by another author so she chose to write under the pen name "Marian Keith". In 1909, she married Donald MacGregor who was one of the founding members of the United Church of Canada. During the time that they were married, they moved several times to places in central Ontario to support her husband's ministerial career. She and her husband spent a fair amount of time in London, Ontario where she wrote seven of her novels. While in London, she formed a Sunday school for girls that was called the "Marian Keith Club". In 1924, she wrote a book called A Gentleman Adventurer which she based on the life of a neighbour, Thompson Smith. Canadian literary scholars have cited this as her best work. In many of her novels, MacGregor sought to portray her connection between religious thought and social conscience in order to improve life for the poor and uneducated. She also wrote about tensions produced between Scottish and Irish settlers and the effects of education and urbanization on rural society. MacGregor authored more than a dozen novels and several biographies, including Courageous Women which she co-authored with Lucy Maud Montgomery and Mabel Burns McKinley. MacGregor was a friend of Montgomery who was also married to a minister. Less