  Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets
launched from the collapsing cores of dying massive stars. They are
characterised by an initial phase of bright and highly variable radiation in
the keV-MeV band that is likely produced within the jet and lasts from
milliseconds to minutes, known as the prompt emission. Subsequently, the
interaction of the jet with the external medium generates external shock waves,
responsible for the afterglow emission, which lasts from days to months, and
occurs over a broad energy range, from the radio to the GeV bands. The
afterglow emission is generally well explained as synchrotron radiation by
electrons accelerated at the external shock. Recently, an intense, long-lasting
emission between 0.2 and 1 TeV was observed from the GRB 190114C. Here we
present the results of our multi-frequency observational campaign of
GRB~190114C, and study the evolution in time of the GRB emission across 17
orders of magnitude in energy, from $5\times10^{-6}$ up to $10^{12}$\,eV. We
find that the broadband spectral energy distribution is double-peaked, with the
TeV emission constituting a distinct spectral component that has power
comparable to the synchrotron component. This component is associated with the
afterglow, and is satisfactorily explained by inverse Compton upscattering of
synchrotron photons by high-energy electrons. We find that the conditions
required to account for the observed TeV component are not atypical, supporting
the possibility that inverse Compton emission is commonly produced in GRBs.
