Distant radio galaxies:: Probes of the formation of massive galaxies

In this paper we review some of the evidence that the hosts of powerful high redshift (1 less than or similar to z less than or similar to 5) radio galaxies (HzRGs) are the progenitors of present day brightest cluster galaxies (BCGs). On the basis of HST imaging we argue that the scenario describing the formation of BCGs consists of at least two important stages. At z > 2 a significant fraction of the stellar mass of a BCG is formed during a massive burst of star-formation. By z similar to 1, well developed massive ellipticals are already observed and from then until the present epoch, the total mass in stars of the BCG will further grow by a factor of order 3, mainly through the accretion of cluster ellipticals.