Slain Soleimani was Iran's second-in-command

By assassinating Iran's top general, President Donald Trump's administration has struck at the heart of Tehran's leadership and escalated the shadow war between the two countries and their allies.

Major General Qassem Soleimani was the second most powerful man in Iran. He answered only to the Supreme Leader Ayatollah Ali Khamenei.

But his influence spread to Iraq, Lebanon and Syria too.

Khamenei -- shown here with Soleimani -- says a "harsh revenge" awaits his killers, and that his death will only increase resistance to the United States.

A holy war, he says.

Soleimani was a legendary figure in Iran -- as head of the Revolutionary Guards' elite Quds Force for two decades, he was the chief architect of Iran's regional alliances -- and its proxy wars.

The Pentagon says Trump ordered the strike to disrupt future Iranian attack plans.

On state TV, the Quds Force spokesman was in tears -- the black band in the corner of the screen marking the start of three days of official mourning.

While Lebanon's powerful Hezbollah said punishing his killers was now the responsibility of all fighters -- that his work would be carried on.

The general was responsible for clandestine operations but also became a celebrity, often shown inspiring militias on the battlefield and negotiating with political leaders.

His forces intervened in the chaos of the Iraqi war and to prevent the toppling of Bashar al-Assad in Syria.

The militia under his influence blamed by the U.S. for attacks on American troops and their allies.

Soleimani helped Iran foster regional alliances as it came under pressure from U.S. sanctions.

From humble rural beginnings, he fought in Iran's war with Iraq in the 1980s, before rising rapidly through the Quds Force ranks.

Soleimani leaves forces and paramilitary proxies that have ample means to respond to his death -- and vast reach.

Revenge is seen as a question of not if, but when and where -- with many expecting Iran to respond forcefully, but perhaps not immediately.