Donald Trump’s cabinet picks are set to undergo Senate confirmation hearings this week to determine whether they’ll make it into the new administration. James Mattis, the president-elect’s pick for secretary of defense, will have his confirmation hearing Thursday at 9:30 a.m. Here are seven things to know about the potential future secretary of defense.

His nickname is Mad Dog. The retired Marine general got his nickname after conducting a number of military campaigns, beginning when he led troops into the Persian Gulf War in 1991. Mattis also conducted the 2004 battle for Fallujah during the Iraq war against Iraqi insurgents. He is reportedly not a fan of the nickname, according to NBC News.

He doesn’t share Trump’s view of waterboarding. “General Mattis is a strong, highly dignified man. I met with him at length and I asked him that question. I said, ‘What do you think of waterboarding?’ He said – I was surprised – ‘I’ve never found it to be useful,’” Trump told the New York Times in November. “He said, ‘I’ve always found, give me a pack of cigarettes and a couple of beers and I do better than that than I do with torture.’” Trump, on the other hand, has been a vocal proponent of waterboarding and said he would utilize it as president.

He is staunchly anti-Iran. The 66-year-old has repeatedly shared his displeasure with Iran over the years.  “I consider ISIS nothing more than an excuse for Iran to continue its mischief. Iran is not an enemy of ISIS; they have a lot to gain from the turmoil that ISIS creates,” he said in 2016. “I would just point out one question for you to look into. What is the one country in the Middle East that has not been attacked by ISIS? One. That is Iran. That is more than happenstance, I’m sure.” During his time as a Marine in 2012, he defined the three greatest threats to the U.S. as “Iran, Iran, Iran.”

GettyImages-624422810 President-elect Donald Trump and retired United States Marine Corps general James Mattis exit the clubhouse after their meeting at Trump International Golf Club, Nov. 19, 2016 in Bedminster Township, New Jersey. Photo: Getty

A legal hurdle could bar him from the position. A federal law on the books states that potential defense secretaries must not have served in active duty for at least seven years. Mattis retired as chief of U.S. Central Command in 2013, placing him three years shy of that requirement. However, it is possible for Congress to overwrite the existing law with a new one in order to instate Mattis as secretary of defense.

He’s known for his punchy phrases. Mattis’ often controversial words have likely contributed to his Mad Dog moniker. “You go into Afghanistan, you got guys who slap women around for five years because they didn’t wear a veil. You know, guys like that ain’t got not manhood left anyway. So it’s a hell of a lot of fun to shoot them,” he said in 2005. “Actually, it’s quite fun to fight them, you know. It’s a hell of a hoot. It’s fun to shoot some people. I’ll be right up there with you. I like brawling.”

He’s never been married. Mattis has never been married, nor does he have any children. His lifelong bachelorhood is the source of his second nickname, reportedly the one he prefers more, the Warrior Monk.

He is extremely well read. Mattis reportedly carries a copy of Marcus Aurelius’ Meditations with him at all times. He has accumulated an extensive collection of books and given away thousands to Marine and local libraries while retaining a personal library of thousands. “He is one of the most urbane and polished men I have known,” retired Army Maj. Gen. Robert Scales said of Mattis. “He can quote Homer as well as Sun Tzu.”