Trunks is the offspring of Bulma and Vegeta, who are both human and Saiyan hybrids. As a child during the Majin Buu arc, Trunks exhibits traits similar to his father, including being cocky, stingy, and mischievous. This may be due to growing up in peace with Vegeta and enjoying the luxuries that came with it. In contrast, Future Trunks grew up without Future Vegeta and in an apocalyptic world, leading him to be more serious and cautious.
Trunks possesses a combination of his parents' personalities - being cocky and proud like his father, as well as spoiled and selfish like his mother. However, later in life, he adopts a personality similar to his future counterparts, acting calmly during battles at the World Martial Arts Tournament and insulting his opponents, much like Vegeta does.