  We report on the discovery of the first ultra metal-poor (UMP) star
2MASS~J20500194$-$6613298 (J2050$-$6613; \mbox{[Fe/H] = $-4.05$}) selected from
the Gaia BP/RP spectral catalog that belongs to the ancient Atari disk
component. We obtained a high-resolution spectrum for the star with the MIKE
spectrograph on the Magellan-Clay telescope. J2050$-$6613 displays a typical
chemical abundance pattern for UMP stars, including carbon and zinc
enhancements. In contrast, J2050$-$6613 shows extremely high [Sr/Fe] and
[Sr/Ba] ratios compared to other stars in the [Fe/H] $<-4.0$ regime.
J2050$-$6613 is most likely an early Population\,II star that formed from a gas
cloud that was chemically enriched by a massive Population\,III hypernova (E $>
10^{52}$\,erg). Such a Population\,III core-collapse hypernova could
simultaneously explain the origin of the abundance pattern of light and heavy
elements of 2MASS~J2050$-$6613 if a large amount of Sr of
$\sim10^{-5}$\,M$_{\odot}$ was produced, possibly by neutrino-driven
\textbf{(wind)} ejecta. Therefore, the abundance pattern of 2MASS~J2050$-$6613
places important constraints on Sr-producing nucleosynthesis sources operating
in the Atari progenitor at the earliest times.
