There is news going around that an anime adaptation of Dragonball Episode of Bardock has been green lit and ready for pre-production. Keep in mind that Episode of Bardock is a short three-chapter manga that ran inbetween the August and October issues of V-Jump – it’s different from Dragon Ball Z: Bardock – The Father of Goku, which is a canonical exposition on the story of Goku’s father, Bardock, and the destruction of Planet Vegeta at the hands of Freeza.
There is no confirmation if the Episode of Bardock manga is canon, since it was done by someone other than Toriyama, but it fits in well with the timeline as it happens immediately after the events in Bardock – The Father of Goku, and also thousands of years before it (explanation below).
Episode of Bardock follows the titular character (who supposedly got vaporized by Freeza in the film) as he finds himself miraculously transported back to Vegeta, millions (or just thousands?) of years in the past. Bardock meets a race of creatures with healing powers, which tended to his injuries. It was not explained in the series as to whether the race will be wiped out by the future Saiyans or if they will eventually evolve into the Saiyans.
Bardock also meets the ancestor of Freeza and Cooler, who invades planet Vegeta, only to find Bardock as its sole defender. Naturally, Bardock is nowhere near as powerful as any of Freeza’s kind and was promptly beaten by the invaders, but Episode of Bardock’s climax will give you a solid explanation as to where the legend of the Super Saiyan started and why Freeza is trying to prevent it from ever happening.