There are evidances about Germanic people, Latins, Gökturks Kingdoms, Scythians, Sarmatians, even about Magyars who came later in Europe, but unfortunatly there are no about proto-Slavs.
Some of them are groups of various peoples. Many today’s Slavic people are descendants of those tribes. However, to determine which tribe was the first speaker of the (proto)-Slavic language is impossible. I’m sure many languages have merged their vocab with Slavic dialects since the division of Slavic and Baltic. Then one of the dialects was standardized (OCS) and expanded to all Slavic lands, which tightened the dialects and probably killed many other languages that were spoken here.
We don’t know almost anything about Proto-Slavic language or tribes, so it’s all just speculations what we’re playing with.
@aaaaa ‘s thread about origin of Slavs has the same value as if we said “Slavs are descentants of Germanics”.