This paper deals with two names of the direct Mojmir line (Great Moravia, 9th–10th century): *Mojьměrъ/*Mojьmirъ and *Svętěpъlkъ/*Svętopъlkъ. In the paper, the author analyzes three hypotheses concerning the origin of Proto-Slavic onymic elements *-měrъ/-mirъ in the Late Proto-Slavic personal name *Mojьměrъ/*Mojьmirъ > Czech-Slovak Mojmír, attested as Moimar, Moymar ʻMojmir I, ruler of Great Moraviaʼ, and Moymir, Moymarius ʻMojmir II, ruler of Great Moraviaʼ: (1) Proto-Slavic *-měrъ < Proto-Indo-European *meh1-ro- ʻglorious, greatʼ, (2) Proto-Slavic *-měrъ < Proto-Germanic, Gothic mērs ʻgloriousʼ, Proto-Slavic *-mirъ being in both cases secondary, Proto-Slavic *-mirъ < Proto-Slavic *mirъ ʻpeace, worldʼ, Proto-Slavic *-měrъ being secondary, which is rejected, as well as two hypotheses concerning the origin of the Proto-Slavic onymic element *-pъlkъ in the Late Proto-Slavic personal name *Svętěpъlkъ/*Svętopъlkъ > Czech Svatopluk, Slovak Svätopluk, attested as Szuentiepulc, Zuentibald, Zuentebald, Sfentopulch, etc. ʻSvatopluk I, ruler of Great Moraviaʼ, and Zentobolch, Zuentibald ʻSvatopluk II, prince of Great Moraviaʼ: (1) Proto-Slavic *-pъlkъ ʻregiment, crowd, etc.ʼ < Gothic or Longobardic fulk- ʻpeople, multitude, armyʼ < Proto-Indo-European *pel- ʻfill, etc.ʼ, which is more popular, (2) Proto-Slavic *-pъlkъ ʻregiment, house [= clan], etc.ʼ (cf. Old Czech meanings and Proto-Germanic fulg- ʻto followʼ) < Proto-Indo-European *plk- ʻto stand by sb.ʼ, which is more probable. After the discussion, the first personal name is reinterpreted as *Mojiměrъ < Proto-Indo-European *moios ʻmy [regiment, house]ʼ + *meh1-ro- ʻglorious, greatʼ, and the latter one as *Svętěpъlkъ/*Svętopъlkъ < Proto-Slavic *svęt ʻglorious, greatʼ (< Proto-Indo-European *ḱwen- ʻto celebrateʼ) + Proto-Slavic *-pъlkъ ʻregiment, houseʼ.