Bardock worked on the Planet Vegeta as a mercenary for the Saiyan Royal Family. For a "common" Saiyan Bardock was quite an exception to the rule with a power level more fitting of a Saiyan Royal, than a run of the mill Warrior.
As with all warrior Saiyans on the Planet Vegeta, Bardock was in employ of the mysterious and powerful Frieza. Frieza ordered Bardock and some other mercenaries in his employ to kill some aliens. As you'll see later in the conclusion Bardock's contact with these aliens brings on unusual powers.
Then at the moment of truth Bardock unleashed his most powerful energy attack toward Frieza. But it was in vain, as Frieza unleashed his own even greater energy atack back at the Saiyan planet, swallowing up Bardock and destroying the Planet Vegeta.
Bardock's efforts did not go unrewarded though, as just before the moment of his demise, Bardock envisioned the death of Frieza at the hands of his Super Saiyan son Goku.