Question: Who named the Torah Portions and when did this start?
Answer: Hi! You’re asking an interesting and difficult question. I’m not sure that anyone named the portions. We don’t even really know where they came from; the Torah itself doesn’t have any specific portion divisions. In Israel they used to have a system of reading the Torah in a three-year cycle, probably what some texts of the Torah (see the Korein edition, for example) divide up as “Sedarim”. In other places, the custom was to finish yearly, and that’s where they began to divide it up into our portions.
As to the names of the portions, many other names have been used. In the time of the classic commentaries of Rashi and Maimonides, for instance, it was common to call the portion we call “Toldos” by the name “V’Eleh Toldos Yitzchak.” The portion of Noach might be called “Eleh Toldos Noach.” The portion of “Shmos” was often called “V’Eleh Shmos,” and so on. In general, one or more of the first words of the portion make up the portion’s name.