I do not know of a single Iranian who was more indispensable to his government’s ambitions in the Middle East. From 2015 to 2017, when we were in the heat of the fighting against the Islamic State in both Syria and Iraq, I would watch Soleimani shuttle back and forth between Syria and Iraq. When the war to prop up Bashar al-Assad was going poorly, Soleimani would leave Iraq for Syria. And when Iranian-backed militias in Iraq began to struggle against the Islamic State, Soleimani would leave Syria for Iraq.

That’s now a problem for Iran. Just as the United States often faces a shortage of human capital—not all general officers and diplomats are created equal, sadly, and we are not exactly blessed with a surplus of Arabic speakers in our government—Iran also doesn’t have a lot of talent to go around. One of the reasons I thought Iran erred so often in Yemen—giving strategic weapons such as anti-ship cruise missiles to a bunch of undertrained Houthi yahoos, for example—was a lack of adult supervision.

Qassem Soleimani was the adult supervision. He was spread thin over the past decade, but he was nonetheless a serious, if nefarious, adversary of the United States and its partners in the region. And Iran and its partners will now feel his loss greatly.