The first inhabitants of the region that is now Equatorial Guinea are believed to have been Pygmies, of whom only isolated pockets remain in northern Río Muni. Bantu migrations between the 17th and 19th centuries brought the coastal groups and later the Fang. Elements of the latter may have generated the Bubi, who emigrated to Bioko from Cameroon and Río Muni in several waves and succeeded former Neolithic populations. The Igbo of Nigeria (mostly Aro) slave traders arrived and founded small settlements in Bioko and Rio Muni which expanded the Aro Confederacy in the 18th and 19th centuries. The Annobón population, originally from Angola, were brought by the Portuguese via São Tomé.

Source: https://en.wikipedia.org/wiki/HistoryofEquatorial_Guinea