"They (U.S.) hit him (Soleimani) in a cowardly way, but with God's grace and through endeavors of freedom-seekers around the world who want vengeance over his blood, we will hit his enemy in a manly fashion," vowed Esmail Qaani, the newly-appointed chief of Iran's elite Islamic Revolutionary Guard Corps (IRGC) – Quds Force, during the ceremony marking the official beginning of his tenure on Monday (January 20).

Sixty-two-year-old Qaani took over the reins of the Quds Force, that carries out the Iranian military's special operations abroad, within hours after his predecessor Qasem Soleimani was killed in a U.S. drone strike near Baghdad airport on January 3.

In a decree appointing Qaani, Iran's supreme leader Ayatollah Ali Khameni called him "one of the most distinguished Revolutionary Guard commanders."

Born in the late 1950s in the holy city of Mashad, Qaani joined the IRGC in 1980, shortly before the Iraqi invasion of western Iran that sparked an eight-year-long war, killing over a million people. It was in the battleground that Qaani befriended Soleimani in March 1982.

"We are the children of war," said Qaani in a 2015 interview to the Islamic Republic News Agency, adding "Those who become friends at times of hardship have deeper and more lasting relations than those who become friends just because they are neighborhood friends."

During the war, Qaani quickly rose through the ranks and became a division commander, overseeing operations in northeastern Iran. He also met then-president Khameni during this time. After the war, he was appointed the deputy chief of the IRGC Ground Forces in 1997.

"Soleimani worked primarily on the western front and Qaani concentrated on Iran's eastern borders. Just as important, Soleimani soon emerged as the charismatic public face of the Quds Force, while Qaani apparently attended to the organization's day-to-day bureaucratic and administrative affairs," wrote Ali Alfonesh, a senior fellow at the Arab Gulf States Institute in Washington, in a research paper published by the American Enterprise Institute for Public Policy.

Qaani was one of the key figures in Iran's involvement in the Syrian civil war; he also aided Afghanistan's Northern Alliance in its fight against the Taliban in the late 1990s.

The new Quds Force leader, who was designated as a terrorist by the U.S. Department for Treasury in 2012 for his alleged role in funding various terrorist groups including Hezbollah, has been vocal about his criticism of Donald Trump, unlike Soleimani who refrained from making public statements on both internal and external issues.

"Threats against Iran will damage America… We have buried many like Trump and know how to fight against America," Qaani said in a 2017 interview with Iranian state media. 

However, some believe that he lacks the hero-like charm of his high-profile predecessor.

"Qaani is uncharismatic and less distinguished military commander than Soleimani, but his operational battlefield experience, network within the IRGC, and long history of acquaintance with supreme leader Ayatollah Ali Khameni qualify him for such an appointment," Alfonesh said.

While questions remain on whether Qaani can fill Soleimani's big boots, some argue IRGC is above any individual.

"Qaani will hit the ground running," tweeted Afshon Ostovar, an assistant professor at the Naval Postgraduate School in the U.S., adding "The IRGC is part of a broader system. It relies much less on individuals than many analysts believe Soleimani's death will have an impact, but there will be no discernible change to Iran's regional network or operations. Revenge aside."

Given the tensions with the U.S. in the Middle East, Qaani has his task cut out – maintaining the Iranian influence in the region while striving for Iran's long-stated policy, which is to drive American forces out.

But the U.S. is attempting to draw a red line for Iranians and has threatened Qaani. On Thursday, the U.S. Special Representative for Iran Brian Hook told Arabic language daily Asharq al-Awsat, "If Qaani follows the same path of killing Americans then he will meet the same fate."