>Mr. Kolomoisky, 58, a mercurial figure in Ukraine who once funded his own militia to fend off pro-Russian insurgents

the scope and type of available power is what distinguishes oligarchs from mere rich businessmen. In that particular case the Kolomoisky dukedom happened to be right next to the insurgency and he, like it were the actual feudal times, had to "raise the fyrd" so to speak to protect his dukedom and the whole kingdom by extension - his forces were among the key ones who blocked the insurgency from expanding further in the first months when the Ukrainian state and army were kind of in disarray.