The main characters of the biographical book "Cheaper by the Dozen" are Frank and Lillian Gilbreth, two industrial engineers and "efficiency experts" who had twelve children together. Eleven of the twelve children are characters in the novel: Anne, Ernestine, Frank, Jr., Bill, Lillian, Martha, Jack, Jane, Fred, Bob and Dan.
While Frank and Lillian had a twelve children, all but Mary, their second-oldest child, was mentioned. Mary died of dyptheria when she was five. The novel acknowledges the presence of a full dozen Gilbreth kids, but Mary's absence is never explained.
Although the parents are the main characters, the book was written by two of the children: Frank B. Gilbreth,
Jr. and Ernestine Gilbreth Carey. It was written and published after Frank, Sr. died while preparing to leave on a trip to Germany. Toward the end of the novel, Jack, the second youngest, sits on the porch and simply says, "Daddy's dead."
Despite the glum conclusion, many of the characters in the book are presented in a comedic light, especially Frank, Sr. Mr. Gilbreth was extremely systematic and efficient. For example, he used two toothbrushes to brush his teeth, claiming it would save time. He also coined the title phrase as it relates to the novel, as a response to people who questioned why he had so many kids. "Well, they come cheaper by the dozen, you know," was his reply.