The White House Chief of Staff is a relatively new office, created in response to the swelling of the executive branch in the 20th century -- either because of increased responsibilities or bureaucratic bloat, take your pick. Washington had one assistant, his nephew, whom he paid out of his own pocket. By Jackson's time, the government paid for the president's staff, which is to say, for one clerk.
Truman was the first chief executive to have a chief of staff, John R. Steelman, though his title was Assistant to the President. During the Eisenhower administration, chief of staff became the formal title of the official who heads the Executive Office of the President of United States (EOP), an entity created by an executive branch reorganization in 1939, the better to manage the sprawling New Deal.
Today, notes the Washington Post in Whorunsgov.com, "the size and budget of the EOP are a bit of a mystery because many of the employees are detailed from other executive agencies. Staff estimates range from 2,000 to 6,000 employees with an annual budget between $300 million and $750 million."
In 60-plus years, holders of the position of White House Chief of Staff have ranged from obscure to notorious. Who remembers Kenneth Duberstein as Reagan's last chief of four? On the other hand, H.R. Haldeman is well remembered for his stint in the Nixon White House, and then prison.