US Presidential political appointee
Source (Wikipedia): White House Deputy Chief of Staff

The White House Deputy Chief of Staff is officially the top aide to the White House chief of staff, who is the senior aide to the president of the United States. The deputy chief of staff usually has an office in the West Wing and is responsible for ensuring the smooth running of the White House bureaucracy, as well as such other duties as the chief of staff assigns to them. In all recent administrations, there have been multiple deputy chiefs with different duties.