  The INvestigating Stellar Population In RElics is an on-going project
targeting 52 ultra-compact massive galaxies at 0.1<z<0.5 with the X-Shooter
spectrograph (XSH). These objects are the perfect candidates to be 'relics':
massive red-nuggets formed at high-z (z>2) through a short and intense star
formation burst, that evolved passively and undisturbed until the present-day.
Relics provide a unique opportunity to study the mechanisms of star formation
at high-z. In this paper, we present the first INSPIRE Data Release, comprising
19 systems with observations completed in 2020. We use the methods already
presented in the INSPIRE Pilot, but revisiting the 1D spectral extraction. For
these 19 systems, we obtain an estimate of the stellar velocity dispersion,
fitting separately the two UVB and VIS XSH arms at their original resolution.
We estimate [Mg/Fe] abundances via line-index strength and mass-weighted
integrated stellar ages and metallicities with full spectral fitting on the
combined spectrum. Ages are generally old, in agreement with the photometric
ones, and metallicities are almost always super-solar, confirming the
mass-metallicity relation. The [Mg/Fe] ratio is also larger than solar for the
great majority of the galaxies, as expected. We find that 10 objects have
formed more than 75% of their stellar mass (M*) within 3 Gyr from the Big Bang
and classify them as relics. Among these, we identify 4 galaxies which had
already fully assembled their M* by that time. They are therefore `extreme
relics' of the ancient Universe. The INSPIRE DR1 catalogue of 10 known relics
to-date augment by a factor of 3.3 the total number of confirmed relics, also
enlarging the redshift window. It is therefore the largest publicly available
collection. Thanks to the larger number of systems, we can also better quantify
the existence of a 'degree of relicness', already hinted at the Pilot Paper.
