  We present evidence for the existence of an old stellar halo in the dwarf
irregular galaxy WLM, an isolated member of the Local Group. The halo consists
of population-II stars, with low metallicities and age $\geq 10^{10}$yr. The
finding of a halo in a dwarf irregular galaxy argues for a generic mode of
galaxy formation that requires a halo in the presence of a disk, regardless of
galaxy size. This implies that formation mechanisms are similar along the
spiral Hubble sequence, and favors the scenarios where the formation takes
place during the original collapse and accretion of the protogalactic gas
clouds. Halo formation also appears not necessarily to be related to the
presence of a bulge or a nucleus, since WLM lacks both of these components.
