This is something you don’t see every day.
It is a high-speed, high-altitude interceptor, in service since 1983 fielded to counter the B-1B bomber, which was designed to operate at low-level, below the radar coverage. Hence, the Mig-31 has quite good low-level capabilities and is equipped with an advanced radar with look-down-shoot-down capability needed to detect low-flying bombers, and data bus, allowing for coordinated attack with other fighters.
Although it is quite obsolete, with top speed of Mach 2.83 and a range of 1,450 km the Foxhound is still one of the most amazing interceptors ever built, often encountered by U.S. and NATO fighter jets during standard routine identification of Russian warplanes over the Baltic Sea.
Here is an interesting video of some Russian Mig-31s refueling midair from an Il-78 Midas tanker.
H/T Lasse Holmstrom for the heads up