Bardock is Goku's true father (I should say Kakarotto's father). He is the only one that knew that Freeza was about to attack the planet Vegeta. When he got back to Vegeta he found that Freeza was there and he challenged him to a duel. He obviously did not know how powerful the Great Freeza was or he would not have commited such a foolish act. Bardock is also the sayain that created the blast of artificial full moon light that gave the sayains the ability to transform at will.