"A Hero Is Born!" (ニューヒーロー誕生！！ Nyū Hīrō Tanjō!!, lit. "The Birth of a New Hero!!") is the four hundred twenty-third chapter of the Dragon Ball manga.
To open the chapter, Gohan flew to Capsule Corporation to ask Bulma for advice to keep his crime-fighting identity a secret. Bulma suggested to make a device to instantly create a disguise for Gohan to wear, to which Gohan happily agreed to. Bulma then asked Gohan to wait for two hours and the disguise will be ready. Asking where Bulma's son was, Bulma answered that he was training with his father, who is planning to make Trunks stronger than Gohan himself. Looking for the training room, Gohan comments to himself about how big Capsule Corporation was. Trunks then appears and says hello to Gohan, who asks Trunks if Vegeta was really training him. Gohan then says hello to Vegeta, to which the Saiyan prince replies to Gohan that he will get rusty if he overlooks his training.
After two hours, Bulma gives Gohan a device resembling a watch to instantly give him a disguise, leading Trunks to comment on how lame Gohan looked while wearing it. Thanking Bulma, Gohan went home. Telling the Flying Nimbus to fly home at maximum speed, Gohan expressed joy that his identity won't be so easily discovered while fighting crime.
The next morning on his way to school, Gohan decided to put on his new disguise, knowing that if he flies to school himself he will be faster than the Flying Nimbus and no one would know who he is. While flying, Gohan noticed a car driving recklessly on a freeway and stopped right in front of it. As the driver and his companion step out of the car and prepare to attack Gohan with a knife, they ask who Gohan was. Gohan replied by striking a pose and calling himself the Great Saiyaman, which prompts the two criminals to start laughing. Angrily stomping on the ground and creating a hole, Gohan tells them he worked hard on that name. Scared of this, the two drivers stopped laughing and agreed to drive safely.