Personality Son Gohan  is Son Gokuh's and ChiChi's first son. Named after his "great-grandfather", who took in and raised Gokuh when he arrived on Earth, he was always his parents' pride. He admits, while training with his father, that he was spoiled and that he should start doing something to earn his status of great fighter. So he did.  After his father's death, he was brought up by Piccolo, who he admires dearly, despite the quite rough way he got treated in. Piccolo prepared him to fight against the Saiyans that were going to arrive on Earth soon (Vejita and his assistant Nappa). Gohan was not very influent in Freeza's defeat, but after Gokuh discovered the amazing energy he possessed, he was the main responsible for Cell's death.  As a teen, he goes to a champions-only school in Satan City, where he meets Videl, whom he will marry. He fights crime, disguised as a super-hero (the Great Saiya Man).  He hates fighting and his mother keeps insisting that he should concentrate on his studies (so that he doesn't grow up to be an ignorant peasant like his father...). He is quite disciplined (unlike his brother, Son Goten) and reveals an amazing fighting energy when he gets angry.

Gokuh holding baby Son Gohan

Teen Son Gohan, in SSJ state

Technique Like his father, Son Gohan can use the KameHameHa technique very effectively. When he defeated Cell, he actually accomplished it using just one hand (he injured one of his arms defending Vejita), with the help of his just deceased father.  Gohan learnt a lot from Piccolo, who trained him during his childhood, after Gokuh died. As any Saiyan, he had a tail that turned him into a large monster upon seeing the full moon. Piccolo pulled it out, to prevent another transformation.  In the battle with Vejita and Nappa, he first fails to support the other fighters in a particular strike, feeling insecure. Later, he deflects a Genki-Dama attack from Kuririn directing it towards Vejita, who had dodged the initial energy ball. Gohan recovers his tail during the battle, turns into a monster and Vejita almost gets killed (eventually, he cuts the tail permanently and escapes in his space capsule).  He reaches SSJ state when practising with Gokuh in the Room of Spirit and Time and this is where he reveals the huge potential he has, storing an amazing amount of energy and releasing it only in moments of extreme anger. When battling with Cell, he shows his real capabilities and reaches what can be called SSJ2 (and is the first one to do so, too).  During his teen years, before the start of the Buu era, he didn't practise much, because his task as Great Saiya Man wasn't very challenging for a SSJ and he was able to take care of the common criminals easily. Buu will force Gohan to shape-up and he will probably learn new techniques as well (more on this as soon as possible).

Roles in the major battles

Battle against:	Role:	Son Gohan when he killed Cell
Vejita	Firstly, Son Gohan failed to be helpful in this battle. He was a young child at the time and his fear was comprehensible. Nevertheless, he was very useful a bit later, when he corrected a Genki-Dama's trajectory and next when he turned into a Saiyan monster and trashed Vejita badly.
Freeza	Gohan had a discrete performance in this fight, mainly because Freeza out-powered him completely. He escaped from Namek in a space ship without his father, taking a seriously injured Piccolo with him. Gokuh told him to do so and remained on the dying planet to destroy Freeza.
Cell	Basically, Gohan killed Cell. After Gokuh gave up in the middle of the fight with Cell, designating his son as the next challenger, Son Gohan stood still, unwilling to fight, explaining that only when extremely angry could he be a match for Cell. The reptile-like creature then sent miniature versions of itself to attack Gohan's friends. Gohan eventually got so furious that he turned into SSJ2 (I think). He killed the Junior Cells effortlessly and beat up Cell until he coughed out #18 and returned to his third evolutionary state. Cell, in a last effort, starts expanding and Gokuh is forced to take him away with Shunkan-Idou. He regenerates itself, though, returns, kills (Future) Trunks, almost kills Vejita (Gohan protects him) and injures Gohan. He then uses all his strength in a huge KameHameHa, with the help of his father from the Otherworld, beating Cell's own KameHameHa and killing the monster.
Buu	In Portugal, we haven't finished watching the series, so I can't yet fill in this section, sorry.