Retired army lieutenant-general Michael Flynn has shaped President-elect Donald Trump's view on "radical Islamic terrorism" and is likely to continue to do so as his national security adviser.

News of his new position broke on Friday, but reports say that he has already been present at Mr Trump's daily intelligence briefings.

As national security adviser, Lt-Gen Flynn would play a critical role in determining the President's response to such matters as defeating militant groups like ISIS and the possible escalation of tensions in the South China Sea.

This role would be a great comeback for the general, who was highly regarded in the military and intelligence communities, especially for his contributions in Iraq and Afghanistan, but who was fired by President Barack Obama in 2014 as head of the Defence Intelligence Agency because of his combative style and bad management practices.

He said in a New York Post op-ed that he was let go because of the "stand I took on radical Islam".

Lt-Gen Flynn co-wrote a book earlier this year titled The Field Of Fight: How We Can Win The Global War Against Radical Islam and Its Allies". In it he says: "I don't believe all cultures are morally equivalent."

In February, he tweeted that the "Fear of Muslims is rational", forwarding a link to a video backing up this statement.

But some have been cautiously optimistic about the appointment.

Senator Jack Reed, a ranking Democrat on the armed services committee, said in a statement that Lt-Gen Flynn could make up for Mr Trump's lack of experience as he is "familiar with the complex set of security challenges we face".

Reports have also highlighted Lt-Gen Flynn's ties to Russia - he took a speaking engagement last year with Russia Today, a Kremlin funded TV network - and his consulting group's lobbying efforts on behalf of the Turkish government.

But what matters most, to Mr Trump at least, is that he was an early and ardent supporter, who had his back when the majority of the security community spurned him.