  We discuss HST FOS ultraviolet spectroscopy and NICMOS near-infrared
photometry of four young super star clusters in the central region of the
irregular starburst galaxy NGC 1569. The new observations coupled with previous
HST WFPC2 photometry and ground-based optical spectroscopy allow us to isolate
and age-date the hot and cool stellar components of these massive clusters. We
analyze the two components A1 and A2 of the brightest super star cluster NGC
1569-A. This cluster received previous attention due to the simultaneous
presence of Wolf-Rayet stars and red supergiants. The FOS spectra provide the
first evidence for O-stars in NGC 1569-A, indicating a young (5 Myr) stellar
component in A1 and/or A2. Comparison with other high-mass star-forming regions
suggests that the O- and Wolf-Rayet stars are spatially coincident. If so,
cluster A2 could be the host of the very young O- and Wolf-Rayet population,
and the somewhat older red supergiants could be predominantly located in A1.
The mass-to-light ratio of NGC 1569-A1 is analyzed in five optical and infrared
photometric bands and compared to evolutionary synthesis models. No indications
for an anomalous initial mass function are found, consistent with a scenario
where this cluster is the progenitor of present-day globular clusters. The
clusters A1 and A2 are compared to clusters B and #30. The latter two clusters
are older and fully dominated by red supergiants. All four super star clusters
provide a significant fraction (20 - 25%) of the total optical and
near-infrared light in the central region of the galaxy. The photometric
properties of the super star cluster population in NGC 1569 resemble those of
the populous clusters in the Magellanic Clouds.
