About 10% of accreting supermassive black holes at the center of galaxies are capable of launching extreme relativistic jets. These AGNs and their jets have been studied for decades, from radio up to gamma-rays. However, many open questions still remain about the processes powering these powerful monsters. When, in the history of time, were the most luminous jets more numerous, and what is their connection with fast supermassive black-holes growth in the early universe? Are the radiating particles leptons or hadrons? Is the so-called ‘blazar sequence’ real or just a selection effect? In this talk, I will highlight how we can tackle some of these open issues through means of multiwavelength studies, in particular exploiting the capabilities of current high-energy experiments.
