  We prove that it is possible to freeze a light pulse (i.e., to bring it to a
full stop) or even to make its group velocity negative in a coherently driven
Doppler broadened atomic medium via electromagnetically induced transparency
(EIT). This remarkable phenomenon of the ultra-slow EIT polariton is based on
the spatial dispersion of the refraction index $n(\w,k)$, i.e., its wavenumber
dependence, which is due to atomic motion and provides a negative contribution
to the group velocity. This is related to, but qualitatively different from,
the recently observed light slowing caused by large temporal (frequency)
dispersion.
