On 24 November 1995 Professor Ivan Zhelyazkov Petkov, Dr. Sc., the Head of the Laboratory of Theoretical Nuclear Physics in the Institute of Nuclear Research and Nuclear Energy (INRNE, Sofia, Bulgaria) passed away. We lost our teacher and wonderful friend.

Professor Dr.Sc. Ivan Zhelyazkov Petkov

Professor I.Zh. Petkov was born in 1932 in Sliven (Bulgaria) and had graduated from the University of Sofia ``St. Kliment Ohridsky'' in 1956. After three years of work for the Institute of Physics of the Bulgarian Academy of Sciences in Sofia, he had been a Ph.D. student of the Moscow State University ``M. Lomonosov''. Later, from 1962 till 1970 he had worked as research fellow and senior research fellow for the Laboratory of Theoretical Physics of the Joint Institute for Nuclear Research in Dubna (Russia). In 1966 he acquired his Ph.D. degree in the same institute.

Since 1970 Prof. Petkov had started his work in the INRNE in Sofia and in the next years he created the Nuclear Theory Group. In 1976 he defended his Dr.Sc. thesis in Sofia and from 1983 he had been Professor in INRNE.

Professor Ivan Zh. Petkov published more than 150 scientific papers, the most of them in the important international journals on nuclear physics and many--body theory, such as Nuclear Physics, Annals of Physics, Zeitschrift f\"{u}r Physik, Soviet Journal of Nuclear Physics and others. He was a coauthor of three monographs in nuclear physics, two of them published in the Oxford University Press: ``Nucleon Density and Momentum Distributions in Nuclei'' (1988), ``Nucleon Density Functional Theory'' (1991) and one published by Springer--Verlag in Berlin ``Nucleon Correlation in Nuclei'' (1993).

The achievements of Prof. I.Zh. Petkov are in various fields. We will mention among them the results on the electron elastic and inelastic scattering on nuclei, the heavy ion physics (and especially some pioneer works on nuclear fusion studies), the optical potential theory, the studies of short-range correlation effects in nuclei, the density functional theory and its applications to nuclear, atomic and molecular systems.

Prof. I. Zh. Petkov was a supervisor of eight Ph.D. students who defended successfully their thesises. He took an important part in the work on substantial subjects developed in two Dr.Sc. thesises defended by his collaborators.

Prof. I.Zh. Petkov reported on important international conferences and meetings in Russia, Denmark, England, France, Germany, Japan and Bulgaria.

Prof. I.Zh. Petkov worked also as Head of the Physics Department of the University of Shoumen ``Konstantin Preslavski'' (1973-1976) giving lectures in Theoretical Physics, Atomic and Nuclear Physics. He was also a lecturer on Nuclear Reaction Theory in the University of Sofia ``St. Kl. Ohridsky''.

Prof. I.Zh. Petkov had been Vice-Director of the Centre of Physics of the Bulgarian Academy of Sciences and a scientific secretary of the INRNE in Sofia for several years.

Prof. I.Zh. Petkov had given the idea the International Workshop on Nuclear Theory (Giolechitsa, the Rila Mountains, Bulgaria) to be organized and held every year and had been the President of the Organizing Committee since 1980 up to 1995.

The Bulgarian science lost one of the distinguished and recognized Bulgarian scientists abroad, as well as one of the initiators of the studies in nuclear structure and reaction theory in our country. He helped many young scientists to find their own way in the nuclear physics and left the Nuclear Theory Group founded by him in INRNE whose works have been accepted and recognized by the physical community abroad.

The memory of Prof. Ivan Zh. Petkov and his contributions will remain.