The grinding war in eastern Ukraine is grabbing global headlines again as President Barack Obama weighs the merits of providing the Kiev government with U.S. weapons and European leaders make a new stab at compromise with Russian President Vladimir Putin. But Ukraine has an unorthodox homegrown weapon that will likely play a much more important role in its future: billionaire businessman Ihor Kolomoisky.

Ranked as Ukraine’s No. 3 oligarch, with a net worth of $2.3 billion in a survey last autumn by Kiev magazine Novoye Vremya, Kolomoisky controls PrivatBank, the country’s largest commercial bank, as well as industrial companies, oil and metals concerns and consumer goods and services such as airlines and television. For many years he ran his empire largely from Switzerland. But after the February 2014 Maidan revolution, he went home to an appointment from then-acting President Oleksandr Turchynov to one of the nation’s hottest seats: governor of his native Dnipropetrovsk Oblast, a Russian-speaking territory that borders the conflict zone in Donetsk province.

But the billionaire’s patriotism may come with a steep price for Ukraine, analysts fear. In a slow-motion conflict in which snarling rhetoric between Kiev and Moscow alternates with cooperation on practical matters, like gas shipments, Kolomoisky seems to go out of his way to inflame passions.

Although Ukraine’s military struggled in the face of separatist attacks last summer, Kolomoisky organized and paid for a private army of sorts, the Dnipro Battalion, which helped hold the line with thousands of troops. An official of the pro-Russian separatist group Donetsk People’s Republic paid Kolomoisky’s troops a grudging compliment, telling the Russian-language version of Forbes magazine, “They are the most organized, motivated and aggressive” among the pro-government forces.

A semirecluse despite his public office, the oligarch makes the most of rare meetings with outsiders, peppering his speech with obscenities and feeding shrimp to the pet sharks he keeps in a tank in his private office. In his first television interview as governor, he described Putin as a “schizophrenic of short stature.” Kolomoisky’s right-hand man, deputy governor Gennady Korban, lately warned Russian investors holding property in Ukraine, saying, “Be afraid. You know our talents. We will find where and how to take from you.”

Although Dnipro and other local militias are supposedly subject to the command of the national Ministry of Internal Affairs, Kolomoisky remains the effective boss of his crack troops, observers say. “His battalions do not really report to the Ukrainian Army commanders,” an official at an international lender in Kiev comments. “This potentially presents a problem for Ukraine.”