Before he was Dr. Seuss, Theodore Geisel was a succesful advertisement illustrator. The library at UC San Diego has an incredible collection of his pre-Dr. Seuss work.
Schaefer Beer
Schaeffer Bock Beer advertisement, Dr. Seuss Collection, MSS 230, Mandeville Special Collections Library, UCSD
Source: libraries.ucsd.edu
General Electric
General Electric advertisement, Dr. Seuss Collection, MSS 230, Mandeville Special Collections Library, UCSD
Source: libraries.ucsd.edu
Ajax Cups
Ajax Cups advertisement, Dr. Seuss Collection, MSS 230, Mandeville Special Collections Library, UCSD
Source: libraries.ucsd.edu
Flit Insect Repellent
Flit advertisement proof, Dr. Seuss Collection, MSS 230, Mandeville Special Collections Library, UCSD
Source: libraries.ucsd.edu