CliffsNotes began in 1958 as $1 reprints of Canadian study guides for 16 plays by Shakespeare.
Sales expanded rapidly as high school students began to buy the slim yellow and black pamphlets.
By the early 1970s the company had created additional study aids—exam reviews, course outlines, law school materials, and test preparation kits for the SAT, ACT, GRE, and GMAT.
Each year he donated 10 percent of the pre-tax profits to local charities and civic organizations (which, on his death, received half of his estate).
After he sold the company in 1999, Hillegass endowed a chair in English at the University of Nebraska.