  We present and use new spectra and narrow-band images, along with previously
published broad-band images, of stars in the Arches cluster to extract
photometry, astrometry, equivalent width, and velocity information. The data
are interpreted with a wind/atmosphere code to determine stellar temperatures,
luminosities, mass-loss rates, and abundances. We have doubled the number of
known emission-line stars, and we have also made the first spectroscopic
identification of the main sequence for any population in the Galactic Center.
We conclude that the most massive stars are bona-fide Wolf-Rayet (WR) stars and
are some of the most massive stars known, having M_{initial} > 100 Msun, and
prodigious winds, Mdot > 10^{-5} Msun yr^{-1}, that are enriched with helium
and nitrogen; with these identifications, the Arches cluster contains about 5%
of all known WR stars in the Galaxy. We find an upper limit to the velocity
dispersion of 22 kms^{-1}, implying an upper limit to the cluster mass of
7(10^4) Msun within a radius of 0.23 pc; we also estimate the bulk heliocentric
velocity of the cluster to be v_{cluster,odot} approximately +95 kms^{-1}.
