Frieza was the first big bad guy in Dragonball Z. He was looking for the Dragonballs so that he could wish for immortality. But in the end he didn't. He also killed a lot if good guys like Vegeta, Krillin, and Dende. He was the evilest bad guy of them all. But Goku kicked his butt, and spared his life. Goku didn't kill Frieza when he had the chance. So Frieza got away and came back to Earth to destroy everyone, but Trunks killed him before he could.