Jan Tschichold

Jan Tschichold was a large influence on 20th century typography. Born in Germany, Jan worked next to Raul Renner, the designer of the type Futura, and became a strong advocate to sans-serif typefaces. He established a standard size of paper and stressed the importance of typographic hierarchy. Later in life Jan refuted back to serif fonts for blocks of copy, but stayed true to sans-serifs and being the most important. He spent a good part of his career designing covers of Penguin Books, over seeing the development of over 500. 

http://www.designishistory.com/1920/jan-tschichold/