Accreting supermassive black holes at the center of galaxies are sometimes capable of powering extreme relativistic jets. When pointed close to our line of sight, these are called blazars. The jet’s peculiar orientation makes these monsters shine as bright as a hundred trillion Suns and enables us to find them at the dawn of time, when the universe was barely 1-2 billion years old. Finding more such sources and understanding their evolution is key to set robust constraints on the evolution of jets and supermassive black holes through cosmic time. This thesis has aimed to: (i) find the most extreme and distant powerful blazars and measure their jet power and black hole mass through multi-wavelength (radio to gamma-rays) studies; (ii) understand the evolution of this source class. In this talk, I will present the core of this thesis with particular highlight on the most recent results on the evolution of the most powerful persistent objects in the Universe.