After a series of meetings with the president-elect, Donald Trump’s transition team has announced the nomination of war hero Gen. James Mattis for its pick as secretary of defense.

The “Mad Dog,” as he is affectionately known by servicemen, will need Congress to pass legislation allowing him to circumvent a rule that requires nominees for the top Pentagon post to be four years removed from active duty. The Trump transition team sees it as a hurdle and not a roadblock to confirmation.

Ahead of that, here are three things to know about the Marine Corps. general:

‘It’s fun to shoot some people’

The Mad Dog is responsible for carrying the Marines to victory in the bloodbath of Fallujah in 2005, something he has called “a hell of a lot of fun.” It echoes some of the epic statements of previous famous commanders such as Gen. George Patton, who Trump has said we need more of.

Gen. George S. Patton Jr., commander of the Third Army, side by side with Gen. James Mattis

Much like the enigmatic Patton, Gen. Mattis is “bookish” and said to have recalled ancient Greek and Roman war heroes and has stated with plain language his intentions of “slaughtering””the enemy, according to USA Today. Whether or not he shares a fondness for writing poetry like the World War II hero has not been reported — but the two do appear to share an immense love for the battlefield.

He is critical of the Iran nuclear deal

Mattis, like Trump and his other allies, has been a vocal opponent of the Iran nuclear deal struck by outgoing Secretary of State John Kerry and the Obama Administration.  That’s been rumored as one reason for his early retirement.

Back in April, he called Iran “the single most enduring threat to stability and peace in the Middle East,” and warned against getting too cozy with the former state sponsor of terror. Trump has promised to rip up the deal as the U.S. president, although it was a multi-nation pact that involved other members of the U.N. Security Council who have a voice.

Defense Secretary Ash Carter is his polar opposite

Former Defense Secretary Robert Gates shakes hands with Gen. James Mattis (Defense.gov)

“The Warrior Monk,” as he has been called in the field of battle, earned his respect the old-fashioned way.

A decorated 44-year military career in which he not only engaged in large-scale battle with the enemy, but led coalition forces as the top commander for the United States Joint Forces Command, NATO’s Supreme Allied Commander Transformation, and the United States Central Command that saw him promoted to the top general over all Middle East affairs.

Conversely, Obama’s top Pentagon official is a civilian and a scientist, with roots in academia.