He is a cruel person who does not care about others' lives as long as he accomplishes his own goals.

Stated in Episode 6 - Galileo Tesoro, he was the only son of his original mom and dad. They were rich and wealthy people who lived in a big mansion. Roberto was once a very kind person like his family. On his birthday, their family held a feast for the three of them to celebrate. While hearing the outsiders, his father brought food to the hungered people. All that was left was a piece of cake, Roberto decided to cut it into three parts.

One day, something caused the family's mansion to get bombed. Roberto was the only person who had lived. Roberto has a change of personality ever since. Seen in a poor hospital, he was adopted by the chief executive of the world famous "Adonimoon Company".

(Source: Galilei Donna Wikia)