Currently all Russian fighters in service were designed during the cold war. They have underwent a number of modifications to the electronics to meet the demand of modern warfare and also some modifications were made to the airframe itself. The last generations of fighters MiG-29 and Su-27 had a lot of growth potential which Russians succesfully utilized. In the last few years when Russian had record high earnings from arm export, they developed new engines and avionics that boosted their machines still have some basic drawback compared to the 5th generation of planes such as exposed intake, lack of stealthness, lack of sophisticated information exchange system.
The 5th generation fighters that Soviets started to develop were never fully completed. S-37 is flying with imcomplete avionics and parts from Su-27 family that were not originally designed for it. MiG-1.42 didn't receive its FCS and the AL-41 engines that were designed specifically for. The lack of funding from the Russian government forces the design bureaus to look for money elsewhere - namely export. However the neglect and lack of funding for the past 20 years had taken their tolls on the aerialnautical industry. Unless foreign partners are involed, we're unlikely to see Russian 5th generation fighters for a long time.
MiG-23 was the succesor of MiG-21, it followed the trend of light weight supersonic fighters and was influenced by F-111 to be equiped with variable geometry wings. It underwent a number of modifications and was exported to many countries from the Soviet block and in the Middle East.
Strategic heavy interceptor
AS the threat of supersonic bombers emerged, namely B-58 and B-X70, Sovietss responded with MiG-25. This was driven by the lack of effective missle defences around cities and the scarce radar and air defences at the vast northern borders. MiG-25 was built as a missile carrier equipped with a powerful radar and engines that guarantees a supersonic cruise speed and near Mach 3 top speed.
Front line superiority fighter
MiG-29 is one of the best know superiority fighter in the world. Thanks to its advanced aerodynamics and powerful engines, it has unparelled manuverbility and agility. After years of underdevelopment in terms of avionics and communication suites, in the past few years, a number of upgrades were introduced including glass cockpits, phased-array radars, improved navigation and fire control suites. Currently the MiG-29 is still one of the most capable fighters around and will continue to serve in the military of a number of cuntries.
Super-sonic heavy interceptor
When the threat of supersonic bombers appeared, the Soviets responded with the MiG-25. Soon, it's drawback became apparent, the lack of sophisticated electronics and the capability of engaging multiple target. MiG-31 was the evolution of heavy interceptors, it retained the near mach 3 top speed, received a state-of-art radar and communication system and were equiped with deadly long range missles. However, since the fall of the iron curtain, heavy interceptors became a lost cause and modifications were abandoned.
5th Generation superiority fighter
At the beginning of the 80s, Soviets started to design the 5th generation figheters and both Mikoyan Gurevich and Suchoj design bureau were asked for proposals. The entire aviation industry was involed, starting from high pressure hydraulics to a number of new aerodynamic configurations. However the breakup of Soviet Union and the ensuing economic crisis severly hampered the developement progress. Only 1 prototype was made and is flying with incomplete equipment and will likely to stay that way.
Long range superiority fighter
In the seventies Americans started to work on the F-15 and F-16, Soviets did not lag behind. They started to work on their own advanced 4th generation fighter and MiG-29 & Su-27 are the fruition of that effort. It was a revolution in terms of both aerodynamics and electronics. Its airframe is the basis of a multitute of other aircrafts such as the Su-27K (Su-33) and Su-27IB(Su-34) and the modernized versions will serve as the backbone of many countries' airforces.
Advanced multi-role fighter
The evolution of warfare required that planes to perform a number of tasks and the lack of operational autonomy and advanced ground attack capabilities of Su-27 became apparent. However a single pilot cannot perform all the duties, so the training version Su-27UB was chosen to be the platform for the multi-role version. Su-30 received a new electronic suite and a glass cockpit. It has been exported to China and India and will also be deployed in the Russian Airforce.
Carrierborne longrange fighter
When Soviets started to build their carriers, a need for carrierborne fighters arose. The STOL Yaks did not perform well and the need to navalize MiG-29 and Su-27 was obvious. The development of Su-27K brought upgrades to both avionics and airframe that gave Su-27K better ground attack capabilities, canard, newer wings as well as more powerful engines. Curently they are not being exported and no significant modernization program is in progress.
Advanced multi-role fighter
Soon after Su-27 started to be fielded, modernizations started. This was soon stalled by the breakup of the Soviet Unio. During the nineties when Sukhoi received large amount of cash through exports, the modernization program restarted. Canards from Su-27K were installed, newer thrust vectoring AL-31F engines were installed and most importantly a new electronic suite were installed. It is currently the most advnaced mass produced figher in the Russian arsenal.
5th generation fighter
S-37 started in the same program as MiG 1.44. Unlike the MiG, Sukhoi decided to go with a radical configuration - foward swept wing. Such configuration gives superior transsonic and supersonic manuverbility, however it causes extreme stress on the materials. S-37 was also planned to be equipped with revolutionary control suite and also a rear facing radar. Thanks to exports, Sukhoi was able to finish the prototype with downgraded electronics and components from Su-27 family and made over 100 test flights.