Mikoyan-Gurevich MiG-21 was supersonic jet fighter from coldwar era. It had unique pencil like design with smooth lines great for high speed flight.
New MIG-X21 is modern stealth version of this great aircraft designed to follow it’s origin but add modern touch while maintaining all advantages of origin aircraft. It has side intakes to improve oxygen usage while flying on stratospheric altitudes. It is much more agile because of quad ruddervators and vector thrust which are great asset while dogfighting. It also has 4 inside missile bays if stealth is more important then heavy load.