  We analyze HST and FUSE ultraviolet spectroscopic data for eleven sight lines
passing through the infalling high velocity cloud (HVC) Complex C. These sight
lines pass through regions with HI column densities ranging from N(HI) =
10^(18.1) to 10^(20.1). From [OI/HI] abundances, we find that Complex C
metallicities range from 0.09 to 0.29 Z_solar, with a column density weighted
mean of 0.13 Z_solar. Nitrogen (NI) is underabundant by factors of (0.01-0.07)
(N/H)_solar, significantly less than oxygen relative to solar abundances. This
pattern suggests nucleosynthetic enrichment by Type II SNe, consistent with an
origin in the Galactic fountain or infalling gas produced in winds from Local
Group galaxies. The range of metallicity and its possible (2 sigma) dependence
on N(HI) could indicate some mixing of primordial material with enriched gas
from the Milky Way, but the mixing mechanism is unclear. We also investigate
the significant highly ionized component of Complex C, detected in CIV, SiIV,
and OVI, but not in NV. High-ion column density ratios show little variance and
are consistent with shock ionization or ionization at interfaces between
Complex C and a hotter surrounding medium. Evidence for the former mechanism is
seen in the Mrk 876 line profiles, where the offset in line centroids between
low and high ions suggests a decelerating bowshock.
