This article is a linguistic analysis of the onomastic layer taken from selected works by Marcin Mortka, which consists of two cycles of stories for children – 5 volumes of stories from the Tappi cycle and 10 volumes of short story collections from the Tappi and Friends cycle. In the analysis, the authors focus on proper names, which in their opinion are the most interesting and extensive linguistic element in Mortka’s work in terms of meaning and word formation. The onyms excerpted from the series about the Viking Tappi (over 200 names in total) are classified by the authors into groups representing different classes: anthroponyms, anthropomorphized zoonyms, toponyms and broadly understood chrematonyms, and the analysis focuses on structure, functions and motivations of these lexical units. At the same time, the authors intend the article to be the first in a series of papers on the onomastics of Marcin Mortka’s works.