"The secretary had every intention of staying because of the critical progress made in national security and other areas," said Steve Goldstein, undersecretary of public diplomacy for the State Department.
"The secretary did not speak to the president, and is unaware of the reason," he added.
Tillerson's departure followed months of disagreements with the White House over staffing and administrative matters at the State Department, which has a large backlog of unfilled jobs. But what may have done him in was a fatal disconnect over what Trump saw as Tillerson's conventional approach to policy matters.
Trump told associates he wanted a secretary of state who looked the part, and he liked Tillerson's camera-ready image and acerbic Texas drawl, real as barbed wire from a man who was named after two 1950s Western movie stars, Rex Allen and John Wayne. He also liked Tillerson's Exxon resume.
But the two men, who did not know each other before Trump's election, never clicked. For Tillerson, despite weekly lunches and frequent phone calls, Trump remained unpredictable and sometimes inscrutable. For Trump, Tillerson became an embodiment of "establishment" naysayers.
Tillerson has no singular foreign policy cause or achievement to his claim, but he had worked to open the door to talks with North Korea. Although Trump dismissively said last year that Tillerson was wasting his time trying to talk to "Little Rocket Man," the summit Trump agreed to last week is partly born of Tillerson's efforts.
A part of his legacy is in his pushback to Trump policies Tillerson considered unwise and argued against, a battle he did not often win. In private meetings with Trump, he told him he thought the United States should stay in the Paris climate agreement and should not break away from the Iran nuclear deal, which Trump has threatened to do this spring.
Tillerson also opposed the unilateral decision to recognise Jerusalem as Israel's capital and move the embassy there. Though he signed documents last week authorising the renovation of an existing consulate, a relatively modest step that theoretically could be reversed in the future, he made clear that security - not politics - was his first concern.
There was an element of anticlimax to Tillerson's exit. Much of his tenure was dogged by rumours he was fed up and ready to quit, or about to be pushed out. But the rumours were persistent enough that the possibility of Tillerson leaving was dubbed "Rexit".
Tillerson consistently, and rather wearily, denied it. In January, he told CNN he would still be around at the end of 2018. As recently as Monday night, while Tillerson was still in the air flying back from a week-long trip to Africa, a top aide said Tillerson was staying put. Tillerson's plane landed at Andrews Air Force Base shortly after 4am.
His exit leaves Defense Secretary Jim Mattis and national security adviser H.R. McMaster, along with Jared Kushner, the president's son-in-law and senior adviser, and White House Chief of Staff John Kelly as the most prominent foreign policy voices, and all are roughly aligned with Tillerson.
Trump said that with CIA director Mike Pompeo as secretary of state, he will be "getting close" to the Cabinet he wants and that he hoped to have the changes in place before his summit with North Korean leader Kim Jong Un.
Tillerson emerged as one of the strongest voices in the administration critical of Russia. For months, he has been saying Russia clearly interfered in the 2016 US election, even as Trump shied away from any critical remarks. On Monday, Tillerson told reporters travelling with him that he was "very, very concerned" with Russia's growing aggression.
Trump seemed to resent pressure to stay the course on such issues as China's trade practices, and the war in Afghanistan and the Iran nuclear deal, those people said.
Tillerson's firing could be a prelude to big policy changes ahead. It comes just two months before the next deadline for the Iran nuclear deal, when Trump must decide whether to reimpose nuclear-related sanctions as he has said he is inclined to do, effectively withdrawing from the multilateral agreement made in 2015 by the Obama administration and other world powers. Tillerson's departure further suggests that Trump is already out the door on the agreement, even as he prepares for talks with Kim.
Although Tillerson supported the approach to the war in Afghanistan that Trump announced last week, he felt no need to frame US goals in the same maximal terms as the commander in chief. Where Trump proclaimed on August 21 that "our troops will fight to win," Tillerson laid out a much more modest agenda.
"I think the president was clear this entire effort was intended to put pressure on the Taliban, to have the Taliban understand that you will not win a battlefield victory," Tillerson told reporters last year. "We may not win one, but neither will you."
Although Tillerson insisted he had what he called a good relationship with Trump, Tillerson and his small circle of aides often found themselves at odds with some Trump aides.
Tillerson had launched a management overhaul at State that is projected to take years, to the annoyance of some senior White House officials eager to dispense political patronage jobs. Tillerson, in turn, was annoyed at the layers of bureaucracy and what he saw as continued chaos and ineptitude months into the new administration, people familiar with his thinking said.
He also complained to friends about competing power centres and a culture of backstabbing that is very different from the top-down corporate culture he left. That same corporate experience gave Tillerson a background in the sensitivities and demands of a large and diverse workforce, and appeared to inform his clear disagreement with Trump over the white supremacist rallies Charlottesville.
Tillerson, who often said he considered himself a lifelong Boy Scout, was not shy about distancing himself from Trump when their values seemed to clash. After Trump asserted that "many sides" were to blame for the violence, Tillerson was asked whether he was "separating himself" from Trump's remarks. Tillerson answered, "I've made my own comments as to our values."
"We do not honor, nor do we promote or accept, hate speech in any form," he said then.
