Volodymyr the Great (958 – 1015), Great Knjaz of Kyivan Rus who introduced Christianity and brought stability to the state. Under his rule, Kyivan Rus reached her zenith:
I think it's not correctly to call them only "Ukrainian" heroes, they're heroes for all Eastern Slavs.
Konstanty Kalinowski is a national hero for Belarussians, Poles and Lithuanians alike but still he is an ethnic Belarussian first. Same with Sviatoslav and Volodymyr, they may be heroes for all Eastern Slavs but in first line they are Kyivans and I don't think I have to tell you where Kyiv is