Great Saiyaman

The Great Saiyaman (グレートサイヤマン; Gureto Saiyaman) is Gohan's alter ego and an attempt to hide his true identity from his classmates when he attended school in Satan City. The Great Saiyaman was first born when Gohan transformed himself into a Super Saiyan in order to disguise himself as he fought some bank robbers on the morning on his first day to school. However, his classmates (and in particular, Videl) began to note strange similarities between himself and the mysterious "Gold Fighter" (as they described his Super Saiyan form). Concerned that his identity might be figured out, but wanting to protect the city from random crime, he approached Bulma and asked her if she could invent a device that could instantly change his appearance. With his new costume ready and easily accessible with the press of a button, he could now protect the city without his identity being easily discovered.
However, despite the new disguise and protection of his identity being discovered, the Great Saiyaman identity still didn't ensure Gohan's identity from being safe. Juggling between his school and superhero life proved to be difficult, and his classmates and teachers noticed that he was gone for a long period of time when he asked for bathroom breaks. Also, Videl proved to be a thorn in Gohan's side, as she was both reluctant to accept assistance from him and most importantly wanted to discover his true identity. At one time, the Great Saiyaman's true identity was in jeopardy of being discovered when he changed from being the Great Saiyaman to his normal form and noticed that his fellow classmate Angela was standing in front of him during his change; however, he was saved when she revealed that she didn't have her contact lenses on at that time and couldn't see anything- and that her big secret about Gohan was the fact that he wears teddy bear underwear.
Gohan's luck ran out when Videl eventually discovered his true identity when she noticed that Gohan had a band-aid to cover up a scratch to the face he received while fighting alongside with her under his disguise. Alternately, in the manga Videl discovers his true identity much sooner. The first time Gohan sneaks out of school to help Videl with some criminals, she recognizes his voice (implying he wasn't altering it like in the anime). She then tricked him into revealing his identity by asking "By the way, Gohan...how'd you sneak out of class?", which he responded to honestly before realizing what had happened. However, she promised him that she would not reveal his identity if he promised her two things: To enter in the World Martial Arts Tournament and to teach her how to fly, to which he reluctantly agreed. During the Tournament however, his friends learned of his true identity when they noticed the great similarities between Gohan and the Great Saiyaman (Gohan forgot to put his bandanna on after turning Super Saiyan in anger after seeing Videl's match with Spopovich). Incidentally on the same day, he transformed into a Super Saiyan again at Kibito's behest, confirming to both Videl and his friends that he was also the Gold Fighter as well. Videl then realized that Gohan was the young boy who also competed in the Cell Games tournament, and therefore questioned whether her dad really won the Cell Games Tournament or not (even going so far as to realize that it was Gohan who defeated Super Perfect Cell in the anime).
The name "Saiyaman" is a reference to his Saiyan heritage. He thought up the name on the spot while confronting two youths who were speeding in a car, and was easily offended when they laughed at his name. Later, the name was frequently mistaken for others, such as the "Great Soyman" or the "Great Singing man", which further aggravated Gohan. He was also noted for his comical poses (comparable to or even more ridiculous than the poses of the Ginyu Force) he would perform when introducing himself, and was generally written off as hilarious or weird. Nonetheless, he was still a respected hero within Satan City. While in this disguise, Gohan still uses his energy-based techniques, such as the Super Explosive Wave and Ki Blasts.