This series began with the arrival of an alien named Raditz at the Kame House (Master Roshi's house). Except, Raditz had a tail... exactly the same as the young Gohan (Gokou's son). He explained that he was of the race of Saiyajins and that his brother was named "Kakarotto," also known as... Son Gokou. Raditz explained that him and Kakarotto had originally come from the planet Vejita, the home planet of the Saiyajins. He went on to say that Gokou was sent as a baby in a small space pod and had a mission. That mission was to ELIMINATE ALL LIFE ON EARTH!!
Gokou and everyone (Gohan, Bulma, Killyn, and the turtle) else denied this new found information as a fact. However, Master Roshi told them that what Radish... I mean, Raditz had said was most likely true. He went on to say that Gokou's grandfather Gohan, wasn't really his grandfather, but in fact, he found the baby Gokou and in a small sphere like ship. Gohan took the baby and raised him as him as his "grandson." Roshi also confessed that Gokou used to have a tail, too, and that he used to be a very angry baby, but Gohan hadn't given up on raising him. But one day, young Gokou had fallen off of a cliff and landed on his head, ever since then, Gokou had been a good, well mannered person.
Raditz had become annoyed at this story and demanded that Gokou help him in destroying the human race. Gokou, of course, tells him "No." Raditz, being a Saiyajin, had become very angry with this and he kidnapped chibi-Gohan (Translation: little Gohan). Soon after Raditz had left, someone arrived... Piccolo.
Piccolo began to say that he had sensed a very large power and for a time believed it was Gokou. While everyone else hid inside the house, Gokou told Piccolo everything and Piccolo agreed to help Gokou in stopping Raditz, but ONLY because the planet was as much Piccolo's as it was Gokou's and Raditz could not harm the planet in anyway.
Bulma gave Gokou the dragon ball radar and said to follow the 4-star dragon ball, since the 4-star ball was sewn to Gohan's hat (yeah, amazingly the hat stayed on Gohan's head even as Raditz flew away speedily, only in anime...). So, Gokou and Piccolo set off to rescue Gohan.
They found Raditz by his pod and demanded to return Gohan. The obvious response from Raditz was... (I think you should know this, if not, email me and give me your home address, so I can hit you up-side the head). Raditz had locked Gohan inside the Saiyajin spacecraft and said they could have him only if they could defeat him, in a very cocky way of course. As Gokou & Piccolo power up, Piccolo then tells Gokou that after they finish with Raditz, it will be their turn to settle their old score. The fight begins.
Gokou and Piccolo get their butts kicked easily, Raditz proves himself to be extremely quick and Gokou & Piccolo don't land a single blow. The two then begin to take off their heavy clothes (the heavy clothes help them train better, do the math) and Raditz is amazed to see that their power levels could rise so much and believes his scouter (a small machine that covers the left ear and with a green lens covering the left eye, used to determine power levels; since they don't know how to sense power levels yet) must be malfunctioning.
The duo do somewhat better against Raditz, but not enough. Piccolo realizes that Raditz's tail must be his weak spot and tells Gokou to hold him by the tail, while he does one of his new techniques. Gokou grabs hold of his tail and Piccolo puts his right index and middle finger to his forehead and begins to charge up. Raditz pleads with Gokou, begging him to let go and he'll never do evil again (yeah right). Gokou being a [sometimes too] nice guy agrees. Raditz slams Gokou to the ground (Never, ever believe the bad guy!!) and mocks him for being so gullible (oh yeah, did ya hear they took gullible out of the dictionary?). Piccolo's pissed, but keeps going with his ki attack (Rough Translation: Ki=energy, stamina, power...). Raditz is busy stepping on Gokou and Piccolo's just about ready.
There is now a small energy ball on Piccolo's fingertips, he extends his arm and yells, "Makankousappu!!!! (I dunno what the hell it means in English, but it is NOT "special beam cannon fire")" and two beams of energy, one in a straight line the other spiraling around the first shoot out of his fingers. Raditz dodges it just in time. Piccolo's pissed and yells, "He's faster than the speed of light!!!" (This is only the beginning of the series, imagine how fast they get in the end of DBGT?). Raditz makes another typical bad guy reply.
Yada-yada-yada, the fighting continues, until... Gohan, still locked within Raditz's space pod, gets very concerned about his father. Gohan gets pissed off at Raditz. Raditz's scouter warns Raditz of a power level that is growing very fast, Gohan. This is when Gohan demonstrates just a fraction of the sleeping power within him. Gohan blows up Raditz's pod and starts crying/screaming, he flies up, and head butts Raditz in the chest. Raditz is down, Gohan's passed out, and Gokou and Piccolo are dumbfounded at what just happened.
Raditz is surprised a child could have such a high power (several hundred, I dunno check the power levels page.). Raditz is alive, but weakened. The fight goes on. Somewhere along the line, Raditz disintegrates Piccolo's left hand (Ow!!!). Gokou has an idea (Yes, Gokou does have something on his head), he wants Piccolo to try another Makankousappu, while Gokou holds Raditz and sacrifices himself. The plan proceeds. Gokou has Raditz in a bear hug, Piccolo's charging up another Makankousappu. Raditz starts going off on some stupid "I'm your brother, please!!" stuff like that. However, Gokou has learned his lesson and holds on tighter.
Piccolo's ready and stronger than ever. Raditz is scared, Piccolo's happy to get 2 birds with one stone, and Gokou's going to go with his first death. And it happens. Piccolo shoots it, it travels through Raditz, through Gokou, and blowing up some mountain in the distance.
Raditz and Gokou are on their last breathes. Raditz mocks Gokou and Piccolo for sacrificing Gokou to stop him. Piccolo goes on to say that they can wish back Gokou using the dragon balls. Raditz laughs and confesses that scouters also count as communicators and that the two remaining (100%) Saiyajins (Gohan's only 1/2 Saiyajin) are listening to the whole fight and will come in one full year. And they are much stronger than he.
Bulma and the others arrive just in time to say bye to Gokou and they'll see him in one year. Gokou's body fades away by Kame-sama's doing.
Killyn decides that the remaining Z team should train as hard as possible for the oncoming threat. Piccolo takes Gohan to train him and awaken his sleeping powers. Killyn says no, then rethinks why he said that. Everyone leaves and only Gohan and Piccolo remain.