  The concordance model of cosmology and structure formation predicts the
formation of isolated very massive stars at high redshifts in dark matter
dominated halos of 10^5 to 10^6 Msun. These stars photo-ionize their host
primordial molecular clouds, expelling all the baryons from their halos. When
the stars die, a relic HII region is formed within which large amounts of
molecular hydrogen form which will allow the gas to cool efficiently when
gravity assembles it into larger dark matter halos. The filaments surrounding
the first star hosting halo are largely shielded and provide the pathway for
gas to stream into the halo when the star has died. We present the first fully
three dimensional cosmological radiation hydrodynamical simulations that follow
all these effects. A novel adaptive ray casting technique incorporates the time
dependent radiative transfer around point sources. This approach is fast enough
so that radiation transport, kinetic rate equations, and hydrodynamics are
solved self-consistently. It retains the time derivative of the transfer
equation and is explicitly photon conserving. This method is integrated with
the cosmological adaptive mesh refinement code enzo, and runs on distributed
and shared memory parallel architectures. Where applicable the three
dimensional calculation not only confirm expectations from earlier one
dimensional results but also illustrate the multi-fold hydrodynamic
complexities of HII regions. In the absence of stellar winds the circumstellar
environments of the first supernovae and putative early gamma-ray bursts will
be of low density ~1 cm^-3. Albeit marginally resolved, ionization front
instabilities lead to cometary and elephant trunk like small scale structures
reminiscent of nearby star forming regions.
