  We present results from a morphological study of the distant X-ray cluster
MS1054-03 at z=0.83. We have obtained a large, two color HST WFPC2 mosaic of
this cluster, and measured redshifts of 186 galaxies in the MS1054-03 field
with the 10m Keck telescope. Of 81 spectroscopically confirmed cluster galaxies
observerd with HST, 13 are merger systems. Most of these mergers will likely
evolve into luminous elliptical galaxies, and some may evolve into S0 galaxies.
If the galaxy population in MS1054-03 is typical for its redshift up to 50% of
ellipticals may have formed in mergers at z<1. The mergers are generally red
and have no detected OII 3727 emission. This result is consistent with the old
stellar ages of ellipticals inferred from other studies. The mergers are
preferentially found towards the outskirts of the cluster, indicating they
probably occur in infalling clumps. A significant overabundance of close pairs
of red galaxies detected in the outskirts of MS1054-03 confirms the large
number of interacting galaxies in this cluster.
