  Most of the observed and simulated galactic bars are symmetric in the face-on
view. However, there are indeed cases of bars that are off-center with respect
to the disk or have an asymmetric shape. The only well-known example showing
both these features is the Large Magellanic Cloud. We report on the
identification of several lopsided galactic bars in the Illustris TNG100
simulation found among a sample of elongated bar-like galaxies studied in the
past. The bars show a clear asymmetry in the face-on view, which is in the
shape of a footprint. We measured the evolution of the different parameters of
the bars' shape and asymmetry as a function of time and find that the asymmetry
is preserved for a few Gyr. It can grow together with a bar or appear later,
after bar formation. We considered two scenarios leading to the formation of
lopsided bars using controlled simulations. In the first, a Milky Way-like
galaxy interacts with a massive companion placed on a radial orbit in the plane
of the disk and perpendicular to the orientation of the bar at the time of the
first passage. In the second, the galaxy initially has an off-center disk and
the growth of the bar and its asymmetry is more similar to the one found in
IllustrisTNG galaxies, where it is also preceded by the presence of an
asymmetric disk. It is thus possible that lopsided bars are born in lopsided
disks, although in some cases, the time difference between the occurrence of
the asymmetry in the two components is quite large.
