The star type that has a surface temperature of 4000 K and a luminosity 1000 times greater than the Sun is a main sequence star, also known as a dwarf star.
Dwarf stars are the most common type of star in the universe, and they are characterized by a surface temperature of between 3000 K and 7000 K. These stars are relatively small and have a mass similar to that of the Sun, but they are much more luminous, with a luminosity that can be 1000 times greater than the Sun.
Dwarf stars are classified into different spectral types based on their surface temperature, with stars like the Sun being classified as G-type dwarf stars. A star with a surface temperature of 4000 K would be classified as a K-type dwarf star.
Dwarf stars are important because they are the primary source of energy for planetary systems, and they are also the primary source of heavy elements that are necessary for the formation of planets and life.