Trunks is the half-human, half-Saiyan son of Bulma and Vegeta, and later becomes the older brother of Bulla.
During the Majin Buu arc, as a child, Trunks displays a cocky and stingy demeanor much like his father. He is also quite mischievous, likely due to growing up in a peaceful environment with his father Vegeta, enjoying all the luxuries life had to offer. This contrasts sharply with Future Trunks, who grew up without his father in a post-apocalyptic world, making him more serious and cautious.
Trunks' personality is a blend of both his parents'. He is cocky and proud like his father and spoiled and selfish like his mother.
In his later years, Trunks develops a personality similar to that of his future counterpart. During and between his battles at the World Martial Arts Tournament, he exhibits calmness when fighting and often insults his opponents, much like his father does.
(Source: Dragon Ball Wiki)
