General Khalifa Haftar, 73, presents himself as Libya's saviour in the face of a growing jihadist threat, but is himself a hugely divisive figure.
He enjoys the support of lawmakers in the internationally recognised parliament in the country's far east, but is opposed by the authorities in the militia-held capital.
Members of the recognised legislature on Monday voted for the removal of an article in a UN-brokered agreement giving the proposed unity government the power to approve top security and military positions.
Many lawmakers are said to oppose the deal because they fear the clause will lead to Haftar losing his post.
The controversial general returned to Libya after more than 20 years in exile in the United States to join the 2011 uprising that toppled dictator Moamer Kadhafi.
Libya has been wracked by conflict ever since, with rival governments and powerful militias battling for control of key cities and oil wealth.
In May 2014, Haftar launched "Operation Dignity" against Islamists in eastern Libya, prompting the then-government to accuse him of trying to stage a coup.
But after Islamists seized Tripoli soon afterwards, forcing parliament to flee to the country's far east, the recognised authorities gradually allied themselves with a figure previously seen as a power-hungry renegade.
In March 2015, the white-haired general with contrasting black moustache was named head of the Libyan army loyal to the recognised parliament.
In an interview with AFP soon afterwards, Haftar said the rise of extremists had pushed the country further "towards extremism and terrorism... stripping Libyans of life, security and development".
He said Operation Dignity was to "answer the repeated calls of the Libyan people for the return of the army to combat terrorism in the region".
Haftar declared before the television cameras on Saturday that the liberation of the eastern city of Benghazi was "imminent" -- a claim he has made before -- and that "the next war would be in Sirte", the coastal stronghold of the Islamic State group.
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From Kadhafi friend to foe
Haftar started his career under Libya's monarchy, graduating from military academy in Benghazi and travelling to the Soviet Union for training.
In 1969, he took part in the military coup that overthrew Libya's royal family and brought Kadhafi to power.
He commanded a unit during Libya's fruitless 1978-1987 war with Chad, but fell from grace with Kadhafi when he was captured by Chadian troops and Tripoli denied he was part of the Libyan army.
The US managed to secure his release, in an operation that is still shrouded in mystery, and offered him political asylum.
Haftar accepted and moved to the United States where he joined Libya's opposition in exile.
His time in the US gave rise to accusations he was linked to the CIA, first from the Kadhafi regime and then from rebel groups during the uprising.
After his return home to join the 2011 uprising, he was named head of the ground forces loyal to the National Transitional Council, the rebellion's political wing.
He commanded a number of officers who like him had defected from Kadhafi's army.
But Haftar never fully won the trust of the interim authorities.
Libya's new leaders feared he could go on to establish another military dictatorship.
His army has also been accused by the United Nations in the past of deliberately trying to sabotage peace talks with its air strikes on militia fighters.
Haftar, in the 2015 interview, denied the military had any interest in meddling in politics, describing it as the "protector against anyone trying to disrupt the democratic process by force".