  We discuss, in the context of the single star scenario, the nature of the
progenitors of Red Supergiants (RSG), of Luminous Blue Variables (LBV) and of
Wolf-Rayet (WR) stars. These three different populations correspond to evolved
phases of Main Sequence (MS) OB stars. Axial rotation and mass loss have a
great influence on massive star evolution in general and more specifically on
the durations of these different phases. Moderate rotation and mass loss,
during the MS phase, favor the evolution towards the RSG stage. Fast rotation
and strong mass loss during the MS phase, in contrast, prevent the star from
becoming a RSG and allow the star to pass directly from the OB star phase into
the WR phase. Mass loss during the RSG stage may make the star evolve back in
the blue part of the HR diagram. We argue that such an evolution may be more
common than presently accounted for in stellar models. This might be the reason
for the lack of type IIP SNe with RSG progenitors having initial masses between
18 and 30 M$_\odot$. The LBVs do appear as a possible transition phase between
O and WR stars or between WNL and WNE stars. Fast rotation and/or strong mass
loss during the Main-Sequence phase prevent the formation of LBV stars. The
mechanisms driving the very strong ejections shown by LBV stars are still
unknown. (abridged)
