  Using a new radio sample, 6C* designed to find radio galaxies at z > 4 along
with the complete 3CRR and 6CE sample we extend the radio galaxy K-z relation
to z~4.5. The 6C* K-z data significantly improve delineation of the K-z
relation for radio galaxies at high redshift (z >2). In a spatially flat
universe with a cosmological constant (Omega_M=0.3 and Omega_Lambda=0.7), the
most luminous radio sources appear to be associated with galaxies with a
luminosity distribution with a high mean (~5L*), and a low dispersion (~0.5
mag) which formed their stars at epochs corresponding to z >~ 2.5.
