Mattis, an active duty general in the Marine Corps who reportedly occasionally reads books, received a lot of good press during his time at Defense, sometimes being referred to as "the only adult in the room" when President Donald Trump's national security and foreign policy team was meeting. Conveniently forgotten are Mattis comments relating to how to "Be polite, be professional, but have a plan to kill everybody you meet." His sobriquet in the Corps was "Mad Dog."
In the media firestorm that has followed upon General Mattis's resignation, he has been generally lauded as a highly experienced and respected leader who has numerous friends on both sides of the aisle in Congress. Of course, the press coverage should be taken with a grain of salt as it is designed less to praise Mattis and more to get at Trump over the decision to leave Syria, which is being assailed by both neoliberals and neoconservatives who believe that war is the health of the state.