Marian Breland Bailey, born Marian Ruth Kruse (December 2, 1920 – September 25, 2001) and nicknamed "Mouse", was an American psychologist, an applied behavior analyst who played a major role in developing empirically validated and humane animal training methods and in promoting their widespread implementation. She and her first husband, Keller Breland (1915–1965), studied at the University of Minnesota under behaviorist B. F. Skinner and became "the first applied animal psychologists." Together they wrote the book Animal Behavior which was first published in 1966, after Keller's death. Childhood and education Born to Christian and Harriet (Prime) Kruse, Marian Ruth Kruse grew up in Minneapolis, Minnesota. Christian, a German immigrant, worked for an automotive supply store, and Harriet was a registered nurse. Bailey's father and then others called her "Maus" ("mouse"), a common German nickname for little girls. After graduating from Washburn High School as her senior class's valedictorian, Bailey went to the University of Minnesota to major in Latin and minor in Greek. Although financial times were difficult as her family had lost everything during the banking collapse of the Great Depression, a full scholarship and a Works Progress Administration award for writers supported her undergraduate education. Before long, she also became a research assistant for B. F. (Fred) Skinner. To meet a science requirement, Bailey took psychology because, as she later explained, "I thought it the least painful science." As a straight-A student, she was recommended for a highly selective psychology class taught by Skinner (the first of what Skinner later called "pro-seminars"), under whom she studied along with George Collier, W. K. Estes, Norman Guttman, Kenneth MacCorquodale, Paul Everett Meehl, and others bound for later fame in their field. With its emphasis on Skinner's new operant training techniques, the course inspired Bailey to major in psychology with a minor in child psychology and to study operant conditioning. Bailey worked as Skinner's teaching and laboratory assistant when he published his pivotal work The Behavior of Organisms in 1938. She trained rats for Skinner, typed lecture notes for him, proofread his book, and even babysat his children. Skinner gave her the final galley proof of his book, which she considered a prized possession. While still an undergraduate student, Bailey met her future husband Keller Breland, who came to call her "Mouse" without knowing that her family called her "Maus". Bailey and others soon decided that her name was Mouse. In