Resumo: We will review the scientific motivation and the early R&D that eventually led the IceCube project to transform a cubic kilometer of natural Antarctic ice into a neutrino detector. The instrument detects more than 100,000 neutrinos per year in the GeV to 10 PeV energy range. Among those, we have isolated a flux of high-energy neutrinos of cosmic origin, with an energy density similar to that of high-energy photons and cosmic rays in the extreme universe. We identified their first source: on September 22, 2017, several astronomical telescopes pinpointed a flaring galaxy, powered by an active supermassive black hole, as the source of a cosmic neutrino with an energy of 290 TeV. Archival IceCube data subsequently revealed a flare in 2014-15 of more than a dozen neutrinos from the same direction. Accumulating evidence suggests that the first cosmic ray accelerator belongs to a special class of active galactic nuclei that is responsible for the origin of the highest energy particles in the Universe.