Which of the following individuals is NOT a current head of a department?

The individual who is not a current head of a department is John Smith. Eric H. Holder, Jr. served as the Attorney General of the United States from 2009 to 2015 during the Obama administration. Thomas Vilsack is the current Secretary of Agriculture. Steven Chu was the Secretary of Energy from 2009 to 2013 but is no longer serving in that role.

While the first three individuals have held significant positions leading government departments in the past or present, John Smith does not correspond to any known current head of a department. The choice reflects a lack of recognition or a fictitious name that does not represent any established officeholder.