We present new and partly preliminary results on the galaxy populations in the massive, X-ray luminous cluster XMMU J2235-2557 at redshift 1.39. We use high-quality optical and NIR data to study the luminosity function of cluster galaxies at different wavelengths (restframe ≈ 3500, 6500, 9000 Å), confirming previous results at lower redshifts showing that the redshift evolution of the characteristic luminosity M* of the luminosity function is consistent with passive evolution of a stellar population formed at redshift z>2. We build a restframe U-R vs R color-magnitude diagram from high-resolution z- and H-band images of XMMU J2235-2557 within R ≈ 700 kpc, finding a tight red sequence already in place. When compared to models of elliptical galaxy formation , the slope and location of the red sequence indicate a formation redshift of z ≈ 3 for the bulk of the stars in red sequence galaxies, at least brighter than M*+l. Spectral energy distribution fitting of multicolor data sampling the restframe ≈ 2700 9000 Å wavelength range consistently indicates that cluster members on the red sequence are already massive galaxies hosting evolved stellar populations.