Media playback is unsupported on your device Media caption In October, Rex Tillerson responded to a report he called Mr Trump 'a moron'

It was no secret in Washington that former US Secretary of State Rex Tillerson and President Donald Trump had a difficult working relationship before Mr Trump fired him.

In October, Mr Trump criticised the former ExxonMobil executive's efforts to open a dialogue with North Korea, telling him in a tweet that he was "wasting his time trying to negotiate with Little Rocket Man".

That same month, Mr Tillerson took the remarkable step of holding a press conference at the Department of State to deny that he had threatened to quit.

But Mr Tillerson notably did not deny reports he had referred to the president as a "moron".

A week later, Mr Trump publicly predicted he would beat Mr Tillerson in an IQ test.

The end of their working relationship, five months later, came abruptly.

A day after the Texan cut short a trip to Africa, Mr Trump announced in a tweet that CIA director Mike Pompeo was now America's top diplomat.

Eye rolls and slouches

When Mr Trump nominated Mr Tillerson to head up the Department of State in December 2016, he was effusive in his praise, calling him "one of the truly great business leaders of the world".

And while the two were careful not to criticise each other publicly, reports soon emerged that they did not see eye to eye.

According to media reports, Mr Tillerson believed the president struggled to grasp the basics of foreign policy.

Mr Trump, meanwhile, is reported to have been irritated by his chief diplomat's body language in meetings.

Mr Tillerson was said to roll his eyes or slouch when he disagreed with his ex-boss' decisions, the New York Times reported.

Media playback is unsupported on your device Media caption Tillerson faced a grilling from senators before taking up the post

During his tenure in Washington, he presided over an unprecedented departure of career US diplomats from the state department.

Former Secretary of State Madeleine Albright, who served from 1997 to 2001, said that diplomats were leaving at "dizzying speed", adding that the vacancies created a US "national security emergency".

Mr Tillerson defended the departures, saying they were part of his plan to "reorganise" the agency, and part of the president's campaign promise to "drain the swamp" of Washington bureaucracy.

He has pointed to the department's "reorganisation" - critics call it "downsizing" - as one his most significant achievements in office.

Oil man and Boy Scout

The 65-year-old spent his entire career working for the world's most valuable publicly traded oil company, ExxonMobil.

He worked his way up to chief executive and later became president of the Boy Scouts of America, during which time the organisation decided to allow gay members to join for the first time.

Mr Tillerson was all set for retirement when President Trump tapped him up for one of his new administration's top roles.

His nomination came amid revelations that US intelligence agencies suspected Russia of covertly attempting to influence last year's US election.

At his confirmation hearing, Mr Tillerson's own links to Moscow, which awarded him the Russian Order of Friendship in 2013, were raked over by senators.

During his time at Exxon, he had forged multibillion-dollar deals with Russia's state oil company, Rosneft.

Mr Tillerson was also known to be friendly with Igor Sechin, Rosneft's executive chairman, who was formerly Mr Putin's deputy prime minister.

Image copyright EPA Image caption Mr Tillerson in his ExxonMobil days (L) with Russian President Vladimir Putin (R)

The Texan oilman was narrowly approved for the state department role, with only a handful of Democrats crossing party lines to back him.

On the eve of his first state trip to Moscow, Mr Tillerson was notably critical of the Kremlin's role in Syria.

But he also publicly spoke out against international sanctions that were placed on Russia over its annexation of Crimea.

Mr Tillerson also kept the state department's press corps at arm's length.

On his first official visit to Asia in March 2017, he allowed only one reporter from a conservative website to accompany him.

"I'm not a big media press access person," Mr Tillerson told the correspondent. "I personally don't need it."

The married father-of-four - worth a reported $325m - can now enjoy a cosy retirement on his Texan horse farm.