When falling into a galaxy cluster, the spiral - rich field galaxy population gets transformed into the characteristic E/S0/dE/dSph - rich cluster galaxy population and this already happens at surprisingly large galactocentric radii around $\sim$3R$_{virial}$. A variety of transformation processes are discussed, their respective importance and timescales. Their relations to the cluster properties, however, remain to be explored. Galaxy transformation processes, transition stages, and timescales can very well be explored by a comparison of deep multi-band imaging for a large fraction of the cluster galaxy population (down to M$^{\ast} + 3$ mag out to redshifts ${z \sim 0.5}$) and of spectroscopy of the brighter members with evolutionary synthesis models. SALT's large collecting area and field of view together with its unique $U$-band sensitivity are ideal in this respect.