Distant radio galaxies as a population of galaxies with active nuclei are of particular interest for research, since current data indicate the presence of supermassive black holes with masses greater than 10$^9$M$_{\odot}$, already formed in these giant stellar systems in the first billion years of the existence of the Universe, and also due to the connection of such systems with protoclusters of galaxies.

For several years, within the framework of the Big Trio project, studies have been carried out on a sample of double radio sources with steep and ultra-steep spectra from the surveys of the Cold experiment on the search for distant radio galaxies.
Optical candidates were found for 94% of the sample, and were not found for the rest of the sources, most likely due to the fact that the objects turned out to be weaker than the limit (R$\leq25^{m}$) of the images obtained with the 6-m BTA telescope.
Optical spectra were obtained for 68% of the sample, and no emission lines were found in 17 candidates, mainly due to the low brightness in the optics.

Three unique distant galaxies with redshift z>3 and high radio luminosity (log(L$_{500\,MHz}$)>28) have been discovered. For these objects, additional studies are still carried out using the MERLIN
and EVN radio interferometers.

Additional studies using modern radio, optical, and infrared sky surveys, including archival data, made it possible to refine the radio structure, optical identifications, magnitudes, redshifts,
and obtain information about the environment of the radio sources for 25% of the sample.