Probably, the most influential White House secretary was George B. Cortelyou who served Presidents Grover Cleveland, William McKinley and Theodore Roosevelt. Cortelyou is credited with creating systems that are still used today in the modern White House press office.
As a young man growing up in Hempstead, Long Island during the 1870s, Cortelyou was persuaded to study shorthand by his first tutor, Mrs. Ephraim Hinds. While attending Georgetown Law School, he landed a job as a stenographer and typist with the U.S. Customs Service, advancing to clerk in the Postmaster General's office in 1891.
Cortelyou caught the attention of President Cleveland who recruited him to serve as his stenographer. He went on to serve President McKinley, and was with the President when he was assassinated in 1901.
Afterwards, President Teddy Roosevelt cajoled Cortelyou into staying on, and lead White House operations into the 20th century. Cortelyou instituted reforms to strengthen communications between the President and the press corps including creating the White House press room, and being the first White House administrator to host briefings and distribute press releases.
Roosevelt later appointed Cortelyou to Secretary of Commerce and Labor in 1903. He resigned in June 1904 to become chairman of the Republican National Committee and manage Roosevelt’s reelection campaign. Cortelyou went on to become Postmaster General in 1905, and Secretary of Treasury in 1907. Many surmise that Cortelyou would not have reached political prominence had it not been for his childhood tutor, Mrs. Hinds, who later became his mother-in-law.