8C 1435+635: a radio galaxy at z = 4.25.

Radio galaxies at red shift z >4 have proved to be very elusive. By searching for objects with unusual radio spectra between 38 and 4850 MHz, and following up with blind spectroscopy, we have discovered the first radio galaxy known with z >4, 8C1435 +635. In this paper we present our observations, discuss the evidence for the redshift, and compare the radio properties of 8C1435 +635 with those of other z> 3 radio galaxies. We also try to assess the likelihood of significant gravitational amplification by a foreground group or cluster of galaxies at z =0.23. Key words: galaxies: active - galaxies: formation - galaxies: individual: 8C 1435+635 - gravitational lensing - radio continuum: galaxies.