The article deals with the documentary reconstruction of the family tree of the famous Khakass archeologist and historian Leonid Romanovich Kyzlasov (1924–2007), whose centenary will be celebrated in the Republic of Khakassia in 2024. The seok (an ethnic lineage) of the Kyzlasovs is called “tag-kharga” and formed the Ulus Dalnekarga of the Steppe Duma of the united heterogeneous tribes in the 19th century. Although there are oral traditions about the origin of the Kyzlasovs, the genealogical information, which is based on historical sources such as church records, censuses, and name lists, has not yet been scientifically verified. The object of the study is the biological family tree of L. R. Kyzlasov, and the subject is the archival and documentary reconstruction of its patrilineal part. The source base of the research was the collections of such archives as the State Archive of the Krasnoyarsk Territory, the National Archive of the Republic of Khakassia, the Archive in Minusinsk, the Manuscript Fund of the Khakassian Research Institute of Language, Literature and History and the Central Archive of the Ministry of Defense of the Russian Federation. For the first time, unique archival documents on the genealogy of the Kyzlasovs are brought into the scientific discourse: according to the Ust-Yes Evdokim Church, a metrical record of 1897 on the birth/baptism of R. A. Kyzlasov, information from the last three censuses of the Dalnekarga genus of the Sagai Steppe Duma for 1832, 1850 and 1858, as well as the facts of the baptism of representatives of the genus in 1854. In the course of genealogical research, an examination of the Kyzlasovs’ family tree schemes was carried out, which were drawn up by several informants based on oral traditions and written documents. The critical analysis of these genealogical materials shows that their information potential requires careful scientific examination, including archival primary sources. The further study of the Kyzlasov family tree will be devoted to the complex genetic and genealogical verification of the data by testing the DNA of the Y chromosome of modern male representatives of the genus. In this way, it will be possible to determine the haplogroup of Kyzlasovs (a genetic genus) and, consequently, to deepen the phylogenetic line of seok “tag-kharga” for thousands of years with the assignment of a family branch on the universal human family tree.