This Review Series pays homage to the contributions of Outstanding Allelopathy Researchers in USSR. It has 4 Parts: Part I (1880-1984), Part II (1904-2000), Part III (1937-2023), Part IV (1937-2023). Part I has been Published in Allelopathy Journal vol 64(2): 95-132, March 2025. The article describes the outstanding results of Allelopathy research (achievements, theoretical and practical developments) during 1902-2000 of USSR scientists. The main biographical data and achievements of scientific activity of outstanding Allelopathy Soviet scientists are given: Alexander Lucianovich Bel’gard, Tikhon Alexandrovich Rabotnov, Ivan Naumovich Rakhteenko, Anna Alexandrovna Chasovennaya, Mikhail Vasilievich Kolesnichenko, Valentina Dionis'evna Roshchina. This group of scientists laid the foundations of (I). Bio- and phytocoenology, (ii). Physiological aspects of allelopathic competitions and its classification, formed directions for the successful introduction of plant species from their possible competitive dominance (T.A. Rabotnov), the influence of root exudates on relations between plants through the rhizosphere, (iii). the basic relations between woody and herbaceous plants and the principles of their landscape combination were determined, (iv). the factors of soil fatigue in perennial vegetation (I.N. Rakhteenko, M.V. Kolesnichenko), (v). Phytoncidal and allelopathic theory of plant interactions in biogeocenoses, (vi). Basis for biotesting of allelopathic effects of plants at the cellular and organismal levels was formed (A.A. Chasovennaya, V.D. Roshchina).