(CNN) There were wild celebrations in the Zimbabwean capital Harare when Robert Mugabe bowed to the inevitable and resigned as President on Tuesday . But as Zimbabweans feted his demise, it was unclear whether they would welcome the man in line to succeed him with such enthusiasm.

Until Mugabe fired him as vice president earlier this month, Emmerson Mnangagwa's entire political career had been hitched to Zimbabwe's 93-year-old former leader.

But Mnangagwa has been eying the presidency and maneuvering to dethrone Mugabe for some time. Sources told CNN that he was instrumental in the military's apparent coup that led to Mugabe's political demise.

Mnangagwa is expected to be sworn in as president by Thursday, according to Simon Khaya Moyo, the spokesman for Mugabe's ZANU-PF party.

'From one tyrant to another'

It is not the first time that Mnangagwa has been in line to lead Zimbabwe

A core member of Mugabe's ruling circle and a combat-hardened veteran of the struggle for liberation from white-minority rule, Mnangagwa was mooted as a potential presidential successor in leaked US diplomatic cables as far back as 2000.

Those cables, part of a huge cache leaked to whistleblowing website Wikileaks by US army soldier Chelsea Manning, paint a picture of a canny political operative, who has surfed the waves of Zimbabwean politics, navigating periods both in and outside of Mugabe's trusted inner circle.

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They also hint at Mnangagwa's dark past. In late 2000, a cable written by Earl Irving , then a US diplomat in Harare, described Mnangagwa as "widely feared and despised throughout the country," warning he could be "an even more repressive leader" than Mugabe if he were to succeed him.

Fear of Mnangagwa stems from his position as Mugabe's enforcer and head of the Central Intelligence Organization (CIO), or secret police, and his alleged role in the 1983-84 massacres of the Ndebele ethnic group in Matabeleland, a region in Zimbabwe's southwest that was a center of political opposition to Mugabe's regime.

The International Association of Genocide Scholars (IAGS), an international nonpartisan organization, estimate at least 20,000 civilians were killed by the CIO and the armed forces.

"Most of the dead were shot in public executions, often after being forced to dig their own graves in front of their family and fellow villagers," IAGS said in a 2011 report.

Kate Hoey, a British Labour MP who has campaigned for years to highlight oppression under the Mugabe regime, described Mnangagwa in a parliamentary debate last week as "probably the one person in Zimbabwe who inspires even greater terror than Mugabe."

Responding later in the debate, Boris Johnson, the British Foreign Secretary, called for elections to choose a new leader. "Nobody wants simply to see the transition from one unelected tyrant to the next," he told the House of Commons, hinting at years of allegations that Mugabe only won elections by rigging the votes.

"We want to see proper free and fair elections next year and that's what we will be working towards."

From low to high

Nicknamed the "Crocodile" on account of his political longevity and survival skills, Mnangagwa has for years been thought to be biding his time, ready to takeover from Mugabe when the nonagenarian finally stepped aside, or died.

His impeccable revolutionary credentials, coupled with his strong support among key parts of Zimbabwe's elite -- specifically within the military and security services -- singled him out as an obvious, and non-controversial, successor.

Photos: The life and career of Robert Mugabe Robert Mugabe is sworn in for his seventh term as Zimbabwe's President in August 2013. He resigned in November 2017 after nearly four decades in power. Hide Caption 1 of 31 Photos: The life and career of Robert Mugabe Mugabe gestures towards the media in Geneva, Switzerland, at a 1974 conference convened to address the civil war in Rhodesia. After being imprisoned for 10 years in Rhodesia, Mugabe attended the peace talks as a leader of the guerrilla movement ZANU-PF (Zimbabwe African National Union-Patriotic Front). Rhodesia was the state that eventually became Zimbabwe. Hide Caption 2 of 31 Photos: The life and career of Robert Mugabe Mugabe speaks to the press in Geneva in 1976. The following year he was elected president of ZANU-PF and commander-in-chief of the Zimbabwe African National Liberation Army. Hide Caption 3 of 31 Photos: The life and career of Robert Mugabe Mugabe holds a news conference in Salisbury -- now Harare, the capital of Zimbabwe -- in March 1980. He had just been elected as the first prime minister of Zimbabwe, helping to form the new country after British rule of Rhodesia came to an end. Hide Caption 4 of 31 Photos: The life and career of Robert Mugabe From left, NBC News moderator Bill Monroe, Newsday's Les Payne, the Chicago Sun Times' Robert Novak and NBC News' Garrick Utley speak with Mugabe during an episode of "Meet the Press" in 1980. Hide Caption 5 of 31 Photos: The life and career of Robert Mugabe Mugabe holds hands with Libyan leader Moammar Gadhafi at the Organization of African Unity summit in August 1982. Hide Caption 6 of 31 Photos: The life and career of Robert Mugabe Mugabe speaks with his first wife, Sally, during an event in Salisbury in 1980. The pair were married until Sally died in 1992. They had one son, who died at age 4. Hide Caption 7 of 31 Photos: The life and career of Robert Mugabe Mugabe meets with French President Francois Mitterand in Paris in 1982. Hide Caption 8 of 31 Photos: The life and career of Robert Mugabe Mugabe is seen with Indian Prime Minister Indira Gandhi in New Delhi in 1983. Hide Caption 9 of 31 Photos: The life and career of Robert Mugabe Mugabe walks hand in hand with American civil rights activist Jesse Jackson during the Summit of Non-Aligned Countries, which Harare hosted in 1986. Hide Caption 10 of 31 Photos: The life and career of Robert Mugabe Mugabe delivers a speech in Harare in August 1986. Hide Caption 11 of 31 Photos: The life and career of Robert Mugabe Mugabe poses for a photo with other leaders at a Commonwealth of Nations meeting in London in 1986. Pictured from left, in the back row, are Indian Prime Minister Rajiv Gandhi, Canadian Prime Minister Brian Mulroney, Commonwealth Secretary-General S.S. Ramphal, Australian Prime Minister Robert Hawke and Mugabe. In the front row, from left, are British Prime Minister Margaret Thatcher, Bahamian Prime Minister Lynden Pindling and Zambian President Kenneth Kaunda. Hide Caption 12 of 31 Photos: The life and career of Robert Mugabe Britain's Queen Elizabeth II toasts Mugabe during a banquet in the Queen's honor in Harare in October 1991. The Queen had last visited the territory that became Zimbabwe in 1947. Hide Caption 13 of 31 Photos: The life and career of Robert Mugabe US President Bill Clinton gestures while talking to Mugabe after a White House meeting in Washington in May 1995. Hide Caption 14 of 31 Photos: The life and career of Robert Mugabe Mugabe marries Grace Marufu on August 17, 1996. Earlier in the year, he was re-elected President after all of his opponents dropped out of the race. Hide Caption 15 of 31 Photos: The life and career of Robert Mugabe British Prime Minister Tony Blair talks with Mugabe in October 1997, before the start of the Commonwealth Heads of Government meeting. Hide Caption 16 of 31 Photos: The life and career of Robert Mugabe Mugabe speaks during the Southern Africa trade and investment summit in Windhoek, Namibia, in October 2000. Earlier in the year, he implemented a controversial land-reform program that saw the seizure of land from some 4,000 white farmers. Hide Caption 17 of 31 Photos: The life and career of Robert Mugabe Mugabe and Cuban President Fidel Castro are seen in Havana, Cuba, in September 2005. Hide Caption 18 of 31 Photos: The life and career of Robert Mugabe South African President Jacob Zuma walks with Mugabe at Harare International Airport in March 2010. Hide Caption 19 of 31 Photos: The life and career of Robert Mugabe Mugabe addresses the 65th session of the United Nations General Assembly in September 2010. Hide Caption 20 of 31 Photos: The life and career of Robert Mugabe Mugabe cuts his birthday cake with his wife, Grace, and son Bellarmine Chatunga during celebrations in Harare in February 2011. Mugabe was turning 87. Hide Caption 21 of 31 Photos: The life and career of Robert Mugabe Robert and Grace Mugabe arrive at the Vatican for the beatification ceremony of John Paul II in May 2011. Hide Caption 22 of 31 Photos: The life and career of Robert Mugabe Mugabe delivers a speech at his party's annual national conference in December 2012. He vowed to overhaul business laws to require 100% black ownership of firms. Hide Caption 23 of 31 Photos: The life and career of Robert Mugabe The Mugabes attend Pope Francis' inauguration Mass in March 2013. Hide Caption 24 of 31 Photos: The life and career of Robert Mugabe Mugabe and Chinese President Xi Jinping participate in a signing ceremony in Beijing in 2014. Hide Caption 25 of 31 Photos: The life and career of Robert Mugabe Mugabe speaks at the ZANU-PF party's annual conference in December 2016. The party endorsed Mugabe as its candidate for the 2018 election. Hide Caption 26 of 31 Photos: The life and career of Robert Mugabe Mugabe reviews the guard of honor during Zimbabwe's 37th Independence Day celebrations in April 2017. Hide Caption 27 of 31 Photos: The life and career of Robert Mugabe Mugabe kisses his wife during Independence Day celebrations in April 2017. In early November, the sacking of Mugabe's longtime ally and vice president, Emmerson Mnangagwa, was seen as a move to potentially clear the way for Grace Mugabe to succeed her 93-year-old husband. Hide Caption 28 of 31 Photos: The life and career of Robert Mugabe Mugabe arrives to preside over a student graduation ceremony at Zimbabwe Open University in November 2017. It was his first public appearance since the military seized control of the nation and placed him under house arrest. Hide Caption 29 of 31 Photos: The life and career of Robert Mugabe Mugabe meets with generals in Harare in November 2017. Military leaders had been in talks with Mugabe over his exit. Hide Caption 30 of 31 Photos: The life and career of Robert Mugabe Mugabe casts his vote in the 2018 Zimbabwe elections. Hide Caption 31 of 31

But this was to dramatically change two weeks ago, when Mugabe sacked Mnangagwa , in a move to shore up the power of his wife and chosen successor, Grace Mugabe.

A statement from the country's information ministry accused Mnangagwa of "disloyalty, disrespect, deceitfulness and unreliability," sending him into hiding amid reports he was attempting to build a coalition to take on Grace Mugabe in the next election.

"One after the other, (Mugabe's) vice presidents and people around him were estranged by Grace Mugabe," said Geoff Hill, author of "What happens after Mugabe?".

"Nobody knows whether it was her, or whether he wanted a safe pair of hands. Either way it was a very unpopular move."

After senior army figures criticized Grace Mugabe's growing power earlier this month, they have succeed in removing her -- and her husband -- from the picture altogether.

"The army very quickly promised to restore the country to democracy, something Zimbabwe hasn't seen for a long time," said Hill. "They want to have a very inclusive government, possible even with (opposition leader) Morgan Tsvangirai coming in as vice president."

After Mugabe's resignation on Tuesday, it was not immediately clear how events would unfold. But one thing seems clear: After three decades waiting in the wings, Mnangagwa is in pole position to ascend to the country's top job.