Osama Bin Laden's right-hand man was hunted for more than 20 years before being killed in a drone strike at the weekend.
Ayman al-Zawahiri helped Bin Laden plan the 9/11 terror attacks and became the leader of terrorist group al-Qaeda after his death in 2011.
Intelligence services had tracked the al-Qaeda leader down to a house owned by a top aide to senior Taliban figure Sirajuddin Haqqani in Kabul, Afghanistan.
His death means that all of the individuals identified as plotters responsible for the 9/11 attack have now been captured or killed.
Biden said al-Zawahiri's death meant he could 'never again' turn Afghanistan, now once again ruled by the Taliban, into a safe haven for terrorists and promised the US would 'make sure that nothing else happens'.
He said: "Now justice has been delivered, and this terrorist leader is no more.
"We never back down. The United States continues to demonstrate our resolve and our capacity to defend the American people against those who seek to do us harm.
"We make it clear again tonight that, no matter how long it takes, no matter where you hide, if you are a threat to our people, the United States will find you and take you out."
As Bin Laden's right-hand man, al-Zawahiri spent the more than 20 years since the 9/11 terror attacks on the run.
Previously indicted for his part in the 1998 US embassy bombings in Kenya and Tanzania which killed 224 people and wounded thousands more, al-Zawahiri evaded capture in 2001 when US forces invaded Afghanistan and toppled the Taliban government.
He would spend more than 20 years on the run from US intelligence, with his whereabouts being unknown for long periods of time.
However, according to US officials he was tracked down in Kabul after months of work from the CIA, who received intelligence in April indicating al-Zawahiri's wife and daughter had been moved to a safe house.
Intelligence services had been keeping an eye out for the re-emergence of al-Qaeda leaders since the Taliban retook control of Afghanistan.
Agents spent months verifying that the terrorist leader was also in the house and built up an idea of his routine, including spotting him spending long periods of time on a balcony of the house.
It was the balcony that the drone strike was targeted at, with the strike being carried out at 6.18am local time on 31 July.
The drone fired a pair of hellfire missiles into the balcony, killing al-Zawahiri, no other casualties have been reported.
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