We present near-infrared photometry and K-band spectra of newly-identified stars in the Quintuplet Cluster, one of the three known massive clusters projected within 50 pc of the Galactic Center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any other cluster in the Galaxy, and over a dozen other stars in earlier stages of evolution, i.e., LBV, Ofpe/WN9, and OBI. One newly identified star may be the second ``Luminous Blue Variable'' identified in the cluster, after the ``Pistol Star.'' While we are unable to provide certain spectral classifications for the five enigmatic Quintuplet-proper stars, we tentatively propose that they are extremely dusty versions of the WC stars found elsewhere in the cluster, and similar to the dozen or so known examples in the Galaxy. Given the evolutionary stages of the identified stars, the cluster appears to be about 3.5 Myr old. The total mass is estimated to be ~ 104 \Msun, and the mass density in stars is >~ a few thousand \Msun pc-3. The newly-identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 1050.9 photons s-1, or roughly what is required to ionize the nearby ``Sickle'' HII region (G0.18-0.04). The total luminosity from the massive cluster stars is ~ 107.5 \Lsun, enough to account for the heating of the nearby molecular cloud, M0.20-0.033. We propose a picture which integrates most of the major features in this part of the sky, excepting the non-thermal filaments. We compare the cluster to other young massive clusters and globular clusters, finding that it is unique in stellar content and age, except, perhaps, for the young cluster in the central parsec of the Galaxy. In addition, we find that the cluster is comparable to small ``super star clusters.''
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