It would be easy to underestimate Valeriy Zaluzhny. When not in uniform, the general prefers T-shirts and shorts that match his easygoing sense of humor. When he first heard from aides to Ukrainian President Volodymyr Zelensky in late July 2021 that he was being tapped to lead the country’s armed forces, his stunned response was, “What do you mean?” As it sank in that he would become commander in chief, he tells TIME in his first interview since the Russian invasion began, he felt as if he had been punched “not just below the belt but straight into a knockout.” George Patton or Douglas MacArthur he is not.

Yet when the history of the war in Ukraine is written, Zaluzhny is likely to occupy a prominent role. He was part of the Ukrainian brass who spent years transforming the country’s military from a clunky Soviet model into a modern fighting force. Hardened by years of battling Russia on the eastern front, he was among a new generation of Ukrainian leaders who learned to be flexible and delegate decisions to commanders on the ground. His dogged preparation in the run-up to the invasion and savvy battlefield tactics in the early phases of the war helped the nation fend off the Russian onslaught. “Zaluzhny has emerged as the military mind his country needed,” U.S. General Mark Milley wrote for TIME of his counterpart last May. “His leadership enabled the Ukrainian armed forces to adapt quickly with battlefield initiative against the Russians.”

That initiative has now taken a key turn in Ukraine’s favor. In Kyiv’s biggest gains since the war began in February, a lightning counteroffensive in the country’s northeast in early September stunned Russian troops, who fled in disarray and ceded vast swaths of occupied territory. Combined with a second operation in the south, Ukrainian forces say they wrested back more than 6,000 sq km from Russian control in less than two weeks, liberating dozens of towns and cities and cutting off enemy supply lines. The Ukrainian army’s deft game of misdirection, touting a counter-offensive in the south before attacking in the northeast, caught Russia off guard. And it validated the Ukrainians’ arguments that intelligence collaboration and billions of dollars in weapons and materiel supplied by Western allies would yield results on the battlefield.

The sudden victories came at a critical point in what had become a grinding war of attrition. As the economic pressures built across Europe and around the world, skeptics were beginning to doubt whether Ukraine could endure a protracted fight. The dramatic rout rattled Moscow, forcing Kremlin propagandists to admit the setback and upping the military and political pressures on Russian President Vladimir Putin. On Sept. 21 he responded by announcing the first mass conscription since World War II, a partial mobilization of up to 300,000 citizens.

Ukrainian and U.S. officials alike believe the war will be longer and bloodier than most imagine. Putin has shown he’s willing to sacrifice his troops and commit atrocities to exhaust his adversary. In a menacing speech, he warned that he was “not bluffing” when he threatened to use everything at his disposal to defend Russia—an allusion to nuclear weapons. The recent Ukrainian offensive may be a turning point, but it is not the decisive blow. “In hindsight, we’ll look at this like the Battle of Midway,” says Dan Rice, a U.S. Army combat veteran and leadership executive at West Point who serves as a special adviser to Zaluzhny, referring to the pivotal 1942 clash that preceded three more years of war.

Zaluzhny is just one of many Ukrainians responsible for the grit and progress of the nation’s outmanned army. Other key officers include General Oleksandr Syrskyi, the commander of Ukraine’s ground forces, who led the defense of Kyiv and, more recently, the counteroffensive in the east, and Kyrylo Budanov, the head of Ukraine’s military intelligence service. But after the President, Zaluzhny has become the face of the war effort. His persona is omnipresent on Ukrainian social media. One widely shared image shows the “Iron General” kneeling in front of the sobbing mother of one of his soldiers, head bowed in grief in front of a casket. In another he flashes a grin presiding over the wedding of one of his servicemen during a lull in the fighting. Fan channels on Telegram have hundreds of thousands of followers, with many changing their profiles to a photo of the general with his hands held in the shape of a heart. “When Zaluzhny walks into a dark room he does not turn on the light, he turns off the darkness,” one viral TikTok video jokes.

It’s hard to predict where the war is headed or the part Zaluzhny will play in the end. But perhaps for the first time, it now seems possible that the army he commands could achieve victory.