The eminent Russian scientist, Full Member of Russian Academy of Sciences, Professor of Moscow State University Khristiansen Georgiy Borisovich passed away on August 4, 2000. He aged 73. G.B.Khristiansen was one of the leading scientists in Cosmic Ray Physics and High Energy Physics. His fundamental contribution in these fields is well known to the world science community. His death means a severe loss for these fields of science. He was the creator of large-scale setups for studying Extensive Air Showers in Cosmic Rays at Moscow and Samarkand Universities, co-creator of the analogous giant setup in Yakutia (Northern Central Siberia). G.B.Khristiansen proposed and developed new effective technique for studying development of individual air showers based on measuring Cerenkov radiation pulse shape, the method which soon became widely used all over the world. While studying Extensive Air Showers he discovered in principle new phenomenon i.e. sharp change of primary cosmic ray energy spectrum slope near 3.10^15 eV (so called "knee"). This result later confirmed by leading world laboratories is one of great importance for Cosmic Ray Physics and Astrophysics. The new method of studying mass composition of primary cosmic rays was also proposed by G.B.Khristiansen. This method based on measuring muon fraction in Extensive Air Showers made possible to reveal a variation of the mass composition from dominantly light nuclei to a composision of heavier nuclei at energies higher than "knee" energy. A series of well-known works of G.B.Khristiansen were devoted to studying Radio Emission by Extensive Air Showers and proof of its coherence and geomagnetic nature, to hadron interaction scaling breaking at ultra high energies, to experimental proof of existence of particles with 10^19 - 10^20 eV energies. In capacity of professor, G.B.Khristiansen brought up some researcher generations, was one of founders of Ultra High Energy Cosmic Ray School. He was always a good friend and patient teacher for every newcomer to his field of science.