In the alternate timeline, all of the Z team members were killed because of two destructive androids, except for Goku who never gets to fight because of a heart infection. The only survivors were Son Gohan and Trunks. Trunks is the son of Vegita and Bulma. Gohan trained him to become stronger and to reach the level of Super Saiyan. One day the androids appeared and, Gohan confident that he can beat them, had enough of the destruction. By protecting the inexperienced Trunks, Gohan knocked him unconscious and fought them alone. Gohan is powerful, but is killed nevertheless. Trunks grieves deeply and vows to one day avenge Gohan's death. Meanwhile Bulma builds a time machine for Trunks so he could go back in the past to find Son Goku. She believes that if he were alive, things would have been different.
Trunks comes to the past twenty years from the future in a effort to change history. Much like his father, he is hard and aggressive. But unlike his father he is very polite and has values. He thinks in conventional ways and is very civilized when making decisions. While Trunks was young, he grew up in awe of the father he never knew. Trunks was always anxious about meeting his father. He was both impressed and disappointed once they met. During the battle of Cell however, Vegita showed emotion upon seeing the death of his son. Vegita then screamed with passion and attacked Cell.
The Z team revived him after Cell was defeated. He decided to return to his timeline once the danger was over. Trunks had trained in that time so much that his power surpassed the two androids in his time. When he returned to the future, he not only took with him the skills to defeat the androids but also the knowledge of the father he loved so much