We present first results on quantitative infrared spectroscopy of the brightest He I emission line stars in the Galactic center. The observed He I and H broad emission lines are caused by extremely strong stellar winds (Mdot ~ 5 to 80 * 10^-5 M_sun/yr) with relatively small outflow velocities (V_inf ~ 300 to 1000 km/s). The effective temperatures of the objects range from 17,000 K to 30,000 K with corresponding stellar luminosities of 1 to 30 * 10^5\L_sun. Strongly enhanced helium abundances (NHe/NH>.5) are found. These results indicate that the He I emission line stars are evolved blue supergiants close to the evolutionary stage of Wolf-Rayet stars. They power the central parsec and belong to a young stellar cluster of massive stars which formed some 5 * 10^6 years ago. Statistical evidence for a concentration of dark mass (~3*10^6\Msun) in the Galactic center is derived from the stellar velocity dispersion.