Sergey Zaryanko 16 - Public domain portrait painting

The Cossacks were a group of predominantly East Slavic-speaking people who lived in the lands of the Dnieper, Don, Terek, and Ural rivers in Eastern Europe. The Cossacks were known for their military skills and their semi-nomadic lifestyle. They were organized into autonomous communities and were known for their martial traditions and their resistance to foreign domination. The Cossacks played an important role in the history of Eastern Europe, and they were involved in many conflicts and wars throughout their history. Today, the Cossacks are still recognized as a distinct cultural group in some parts of Eastern Europe. Cossacks had a tradition of independence and finally received privileges from the Russian government in return for military service. Originally (in the 15th century) the term referred to semi-independent Tatar groups, which formed in the Dnieper region. The term was also applied (by the end of the 15th century) to peasants who had fled from serfdom in Poland, Lithuania, and Muscovy to the Dnieper and Don regions, where they established free self-governing military communities. In the 16th century, there were six major Cossack hosts: the Don, the Greben (in Caucasia), the Yaik (on the middle Ural River), the Volga, the Dnieper, and the Zaporozhian (mainly west of the Dnieper).

Sergey Zaryanko (1818–1870) was a Russian inventor, engineer, and scientist. He is best known for his contributions to the development of early electric lighting systems. Zaryanko constructed one of the earliest electric lamps in 1860, which he called the "electric candle." This device used a carbon filament enclosed in a vacuum tube and illuminated when an electric current passed through it. Zaryanko's work on electric lighting laid the groundwork for further advancements in the field, leading eventually to the development of practical incandescent light bulbs. However, his contributions were somewhat overshadowed by those of other inventors like Thomas Edison and Joseph Swan, who achieved greater commercial success with their own versions of the incandescent light bulb.