  We report on a long (250 ks) NuSTAR observation of the bright quasar RBS 1055
performed in March 2021, and archival XMM-Newton pointings (185 ks) taken in
July 2014. An optical spectrum of the source taken with the Double Spectrograph
at the Palomar Observatory, quasi-simultaneous with the NuSTAR observations, is
also analyzed. We find that the two-coronae model, in which a warm and hot
corona coexist, well reproduces its broad band spectrum, with temperatures
kT$_e=0.12^{+0.08}_{-0.03}$ keV, kT$_e=30^{+40}_{-10}$ keV and Thomson optical
depths $\tau$=30$_{-10}^{+15}$ and $\tau$=3.0$_{-1.4}^{+1.0}$ for the former
and the latter component, respectively. We confirm the presence of an intense
Fe K$\alpha$ emission line (EW=55$\pm$6 eV) and, when a toroidal model is
considered for reproducing the Compton reflection, a Compton-thin solution with
N$_{\rm H}=(3.2^{+0.9}_{-0.8})\times10^{23}$ cm$^{-2}$ for the circumnuclear
reflector is found. The analysis of the optical spectrum reveals a likely
peculiar configuration of our line of sight with respect to the nucleus, and
the presence of a broad [O III] component, tracing outflows in the NLR, with a
velocity shift $v=$1500$\pm100$ km s$^{-1}$, leading to a mass outflow rate
$\dot{M}_{\rm out}=25.4\pm1.5$ M$_{\odot}$ yr$^{-1}$ and outflow kinetic power
$\dot{E}_{\rm kin}$/L$_{\rm Bol}$ $\sim$0.33%. We estimate the BH mass to be in
the range 2.8$\times$10$^{8}$-1.2$\times$10$^{9}$ M$_{\odot}$, according to
different BLR emission lines, with an average value of
<$M\rm_{BH}$>=6.5$\times$10$^{8}$ M$_{\odot}$. With an Fe K$\alpha$ which is
3$\sigma$ above the value predicted from the EW-L$_{2-10\ \rm keV}$ relation
and an extreme source brightness at 2 keV (a factor 10-15 higher than the one
expected from the optical/UV), RBS 1055 confirms to be an outlier in the
X-rays, compared to other objects in the same luminosity and redshift range.
