President-elect Donald Trump announced that he will nominate retired Marine Corps General James 'Mad Dog' Mattis to be his defense secretary.

He is known as "Mad Dog" for his tough talk and bluntness, and is also well-respected among the military ranks and in Pentagon.

Trump made the decision public to nominate Mattis, who retired in 2013, at an Ohio rally on his first day of "thank you tour."

"I don't want to tell you to this, I refuse to tell you, don't let it outside of this room. I will not tell you that one of our great great generals, don't let it outside, we are going to appoint Mad Dog Mattis as our Secretary of Defense and we're not announcing it until Monday so don't tell it to anybody," he joked with the reporters.

Trump told the New York Times, that Mattis made a strong case against torture, which surprised and impressed him.

"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 [torture]? He said - I was surprised - he said, 'I've never found it to be useful.' He said, 'I've always found, give me a pack of cigarettes and a couple of beers and I do better with that than I do with torture.' And I was very impressed by that answer. I was surprised, because he's known as being like the toughest guy," he said.

Sources in Pentagon, who know him and are familiar with the workings of the system, approved of the nomination of Mattis.

"The president-elect is smart to think about putting someone as respected as Jim Mattis in this role," a former senior Pentagon official was quoted as saying by The Washington Post. "He's a warrior, scholar and straight shooter - literally and figuratively. He speaks truth to everyone and would certainly speak truth to this new commander in chief."

He will require a special waiver from Congress before his confirmation as the defense secretary, because the rule mandates that the secretary must have retired at least seven years before being nominated for the post.