Homeland Security Secretary John Kelly speaks at a news conference at the U.S. Customs and Border Protection headquarters in Washington, Tuesday, Jan. 31, 2017, to discuss the operational implementation of the president's executive orders. Andrew Harnik/AP Retired Marine general John Kelly sprung into action in his first week as White House chief of staff, attempting to impose a military-like rigor upon the staff of the notoriously chaotic West Wing.

Kelly, so far, has overseen the dismissal of bombastic communications director Anthony Scaramucci, ensured that President Donald Trump's visitors make appointments before entering the Oval Office, and insisted that even the most senior members of Trump's inner circle report to Kelly instead of directly to Trump.

It's an uncharacteristic modus operandi for the famously free-wheeling and impulsive president, but Kelly's presence in the West Wing has already had a discernible effect.

Here's everything you need to know about the retired four-star Marine general who served for 45 years before making his way to the West Wing: