Retired general James "Mad Dog" Mattis ─ who for years oversaw US war efforts in the Middle East and was tapped Thursday by President-elect Donald Trump as his new defence secretary ─ did not come by his nickname lightly.

Mattis, 66, commanded a Marine battalion during the First Gulf War and a marine division during the 2003 invasion of Iraq. In 2010, the tough-talking native of Washington state was named to head the US Central Command.

That gave him authority over troops in Iraq, where he helped develop a counterinsurgency approach before overseeing the US withdrawal, and Afghanistan, where he implemented a troop surge.

It also gave him responsibility for an area including Syria, Yemen and Iran.

Previously, the four-star general led the US Joint Forces Command and a Nato command charged with preparing the alliance's forces to meet future challenges.

A colourful commander, he earned the nickname "Mad Dog" with his battle-hardened swagger and the sort of blunt language Marines are famous for.

He has been quoted as saying, "Be polite, be professional, but have a plan to kill everyone you meet."

Trump announced the nomination Thursday at his first post-election rally in Ohio.

"We are going to appoint 'Mad Dog' Mattis as our secretary of defence," Trump told a large crowd of supporters in Cincinnati.

"He's our best. They say he's the closest thing to (World War II-era) general George Patton that we have," Trump said,

If confirmed by the Senate, Mattis will be the first recently retired general to serve as Pentagon chief since George Marshall in 1950, who served under president Harry Truman.

'Warrior Monk'

Mattis's salty language has at times gotten him into hot water, such as when he said during a panel discussion in San Diego, California in 2005: "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 no manhood left anyway. So it's a hell of a lot of fun to shoot them."

He later apologised for those words.

But for all the bluster, Mattis has a cerebral side. He has issued required reading lists to Marines under his command, and instructed them that the most important territory on a battlefield is the space "between your ears."

A scholar of warfare, he is said to have a personal library of more than 7,000 volumes. And as a lifelong bachelor, he has another nickname: the 'Warrior Monk.'

Like Lieutenant General Michael Flynn, Trump's choice as national security adviser, Mattis has been highly critical of the multination agreement reached last year with Iran to curtail its nuclear program.

But while Trump has spoken positively of working with President Vladimir Putin of Russia, Mattis has warned that Moscow wants to "break NATO apart."

Senator John McCain of Arizona, who chairs the Armed Services committee that would hold confirmation hearings for the next defence secretary, has said Mattis is "one of the finest military officers of his generation and an extraordinary leader."

But to serve as defence secretary, Mattis also would need a waiver of a law that bans uniformed military officers from serving as secretary of defence for seven years after leaving active duty.

The law is intended to ensure the bedrock notion of civilian control of the nation's military.

Marshall was granted the same waiver in 1950.