Chasing the most powerful blazars

High-redshift blazars are some of the most extreme sources in the Universe. With jet power exceeding 10^47 erg s-1, they host billion solar masses black holes and are found up to when the Universe was only two billions years old. These sources are of great astrophysical interest as they provide us crucial information about the origin and growth of supermassive black-holes in the early Universe. Detections in the hard X-rays and gamma-rays are desired to find the most powerful objects of this class. With the advent of the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Fermi Large Area Telescope (LAT), it has been possible to increase the sample of high-redshift blazars and to constrain more accurately their physical properties. The improved sensitivity of the LAT has also allowed gamma-ray detection of such sources up to redshift 4.3. Here we present the latest high-redshift blazar detection with NuSTAR and the LAT, and discuss some of their implications.