Qassem Suleimani was the Prince of Iranian Terrorism. To the end, he remained very close to the Supreme Leader and ran an effective "Shia Foreign Legion" of Iran’s own creation that employed militants from Iraq, Syria, Libya, Yemen and beyond.
Indeed, US authorities say the decision to kill Suleimani was the result of unique intelligence revealing he was travelling the region co-ordinating an imminent set of attacks targeting Americans in Iraq, Syria, Lebanon and elsewhere in the region.
If ever there was a case that removing one man could have a truly detrimental effect on an organisation, this would be it.
But despite the loss of such a dominating presence, the Quds Force that he headed remains a large and professional organisation. He had multiple deputies with years of experience.
The Quds Force and its proxies, notably Hezbollah, will continue to pose a very capable operational threat - he was not the one personally pressing the detonator.
The United States could face a more direct threat from these groups as a result of the successful US airstrike against Mr Suleimani in Baghdad, even though the most likely short-term response will be in the region and include turning up the heat in Iraq.
The intelligence assessment has been that Iran and its proxies would not carry out attacks within the US unless it was seen to be doing something directly against Iran. The assassination of Qassem Suleimani would certainly fit into that category.
A case in New York City underscores the potential for a terrorist reprisal attack by Iranian proxies. Ali Kourani, a Lebanese immigrant to the United States was convicted of secretly leading a sleeper cell for the Islamic Jihad Organisation (IJO), the Hezbollah wing responsible for offensive operations outside of Lebanon.
Kourani, who in December was jailed for 40 years, said he would most likely be called on to launch an attack if the US took some kind of action against Iran, Hezbollah or its leaders.
Following the arrest of Kourani, the director of the US National Counter Terrorism Centre, Nicholas Rasmussen told reporters in in October 2017 that Hezbollah was “determined to give itself a potential homeland option as a critical component of its terrorism playbook."
“This is something that those of us in the counter-terrorism community take very, very seriously," he added.
Two other men allegedly connected to the IJO have been arrested in the New York area, but have yet to be tried. Although the pair and Kourani were based in the United States, they were involved in activities all around the world, demonstrating the global reach of the organisation.
Two other Iranians pleaded guilty in November last year to spying on dissidents from the National Council of Resistance of Iran (NCRI) in New York and Washington. They also carried out a surveillance operation of Jewish institutions in Chicago.
One of the reasons why the threat of an Iranian-backed attack does not necessarily diminish with the death of the Quds Force head is because the Iranian security establishment has a tradition of rewarding even brazen initiative. This was one of the potential explanations for an attempted plot in 2011 to assassinate the then Saudi ambassador to the United Nations Adel Al Jubeir, which was only thwarted by good fortune.
Tehran has for decades been dispatching operatives to Europe to carry out assassinations of opponents to the regime and other acts of terrorism.
An Iranian diplomat based in Vienna is awaiting trial in Belgium over an apparent attempt to bomb an NCRI rally in Paris. The gathering was attended by Donald Trump’s lawyer Rudolph Giuliani and the former House Speaker Newt Gingrich. It was just another example demonstrating how active Iranian intelligence operatives have been on the continent.
But there is also a message about what the deterrent effect will be for those charged with carrying attacks outside of Iran.
Many there thought that Mr Suleimani was untouchable. It was previously reported that the US and its allies had him in their sights on several occasions and decided not to take action.
His death now is testament to US intelligence and military prowess and sends the message that nobody is safe from potential attack. When you’re looking over your shoulder all the time – and you know you’re not untouchable - it affects your ability to operate.
Dr Matthew Levitt is a former US Treasury official and the director of the counter-terrorism and intelligence programme at the Washington Institute for Near East Policy. He is the author of Hezbollah: The Global Footprint of Lebanon’s Party of God.