Raditz is the older brother of Goku and uncle to gotten and Gohan. In the start of Dragon ball Z, Raditz arrives on Earth in a space pod, in search of a man named "Kakarot," later revealed to be Goku. After he incapacitates a farmer who found his space pod, Raditz detects a power reading on his Scouter and assumes it is Goku. He tracks down the source of the energy and comes face to face with Piccolo, Goku's mortal enemy at the time. Raditz asks Piccolo where he can find "Kakarot", but Piccolo refuses to tell him, warning him to leave Earth at once. Raditz laughs at Piccolo, who fires a powerful attack at Raditz, leaving him unscathed, only managing to "singe some of his leg hair," as Raditz puts it, which shocks Piccolo. Just as Raditz prepares to destroy Piccolo, he detects another Power level, and this time, he knows that it is Kakarot, the one he is looking for. Piccolo's first attempt to blast Raditz, Raditz tracks the power level down to the Kame house, where Goku was introducing his son Gohan to Bullma, Krillin, Master roshi, and turtle, while also enjoying a reunion. Raditz identifies Goku as Kakarot, and informs Goku that he is his big brother, who arrived on Earth to find him. When Goku asks where Raditz came from, Raditz tells Goku that they are both Saiyan warriors, and tells him the history of the Saiyan race including the Planet Trade Organization's practice of conquering planets and selling them for profit. Goku and Krillin express their disgust at Raditz and tell him to leave, which results in Krillin getting attacked into Kame House, with Raditz showing his tail, one just like Goku used to have, and what Gohan has. When it becomes clear to Raditz that Goku is not coming with him, Raditz kidnaps Gohan (who still has a Saiyan tail) and holds him for ransom. He informs Goku that if he ever wants to see Gohan again, he should eliminate one hundred Earthlings and bring them to Raditz by the next day. Laughing, Raditz flies off with Gohan in his hands.
Later, he shuts the crying Gohan in his attack ball, unable to stand his crying. Raditz is surprised to find that his scouter reported a power level of 710 for Gohan, which Raditz dismissed as a malfunction because it would mean that the child was even stronger than his father. Shortly afterwards, Raditz sees Goku and Piccolo who have joined forces to beat him, and since his scouter accurately warned him of their approach, he came to the realization that Gohan may actually be as strong as his reading said.