Plot Overview
When on the losing side against the demonic creature Janemba, Goku and Vegeta decided to put their differences aside and attempt to fuse by means of the Metamorian based, Fusion Dance technique. Their first attempt however, resulted into a failure, when Vegeta didn't extend his index finger. One of the conditions for a successful fusion is that both fighters need to execute a pose, in perfect symmetry. The slightest error can cause the fusion to fail. The result was, a fat, useless warrior, going by the name of Veku. Somehow, Veku managed to survive the fusion's duration and after a second, this time successful attempt, Gogeta was born.
He wasted little time dispatching of Janemba. After a few crippling body shots, he launched his signature attack, the "Soul Punisher". This attack is not intended to actually destroy the enemy, but just to purify their soul. In Janemba's case, the psycho ogre, who was responsible for Janemba's creation, re-appeared after the Soul Punisher did its job and filtered out the negative energy that possessed his being.
In Dragonball GT, Gogeta makes his second appearance. This time, as a Super Saiyan 4 to fight the Lord of the Shadow Dragons, Omega Shenron. Gogeta's power proved superior as compared to the Dragons', but after a short fight, the fusion dissolved right when Gogeta was about to deliver the final blow. The huge power level of Gogeta's Super Saiyan 4 severely diminished the duration of the fusion, an adverse effect of this method, previously encountered by Gotenks during his fight against Majin Buu.
Like a typical full blooded Saiyan, Gogeta has black hair and black eyes in his regular form. Note that this stage wasn't actually shown during either of his appearances. As a Super Saiyan, his hair turns golden and his eyes turquoise. As a Super Saiyan 4, his fur has a crimson red color, his hair is also red, and his eyes turn blue. Unlike his Potara Earrings counterpart Vegito, Gogeta's clothing has no reference to that of his ingredients. Instead, he appears in traditional Metamorian clothing, like every product of the Fusion Dance does.
 Soul Punisher
As a result of being a Goku/Vegeta fusion, Gogeta possesses each of their respective techniques and abilities. His signature move is the Soul Punisher. In other versions, this ability is also known as Rainbow Sparkling Blast, or Stardust Breaker. This ability is used to purify the souls of evil creatures, such as Gogeta's opponent in movie 12, Janemba.
 Big Bang Kamehameha
In GT, Gogeta was automatically in his Super Saiyan 4 form, as Goku and Vegeta fused at that level. He uses a special move, called the Big Bang Kamehameha, a combination of Vegeta's Big Bang attack and Goku's Kamehameha.
 Other Media Appearances
Gogeta also appears in a large amount of video games, for example the Budokai, and Budokai Tenkaichi series.