Ernesto Lopez is the oldest son of Adriana and Mr. Lopez, and the oldest brother of Luis Fernando Lopez and Leta Lopez-Wilkinson. He was abandoned by his father along with his brother and sister. Ernesto dislikes Luis, believing that he is drug dealing trash. He moved out of the city and started a family, and a job as an accountant. His siblings dislike him, believing he is a "prick", as he apparently never sends money to his mother and only calls her twice a year. Luis makes fun of his wife as well.
Whenever Luis get drunk alone in either Maisonette 9 or Hercules, he will drunkenly mention that Ernesto is an asshole.
During one of the Club Management side missions, Dessie asks Luis to go pick up the Blue Brothers and bring them back to Maisonette 9. Luis complies, but states he's only doing so because his niece is crazy about them. Considering the fact the Ernesto and Luis hardly talk, and that his children think that their uncle Luis is dead, it can be inferred that it is Leta's children he is talking about.
During the Drug Wars missions, Henrique will sometimes question Luis about Ernesto's whereabouts. Luis answers that he doesn't know where Ernesto is and that he doesn't give a fuck.
At one point, Ernesto sends Luis an email insulting him and saying that he should come back to Liberty City to deal with him. If Luis replies negatively to the email, he will respond saying that he'd love for Ernesto to come back and deal with him, and then asks why doesn't he try to send money to their mother.
There are numerous pictures of Ernesto in his mother's house. They are rather hard to view however, as they are only featured in cutscenes.
As mentioned above, if the player should look at Ernesto's pictures in his mother's house, it can be seen that they feature different characters. One, for example, wears a beige suit, is wearing a fedora, and has extremely dark skin, implying he is African-American which is obviously untrue. Another picture shows another version of Ernesto wearing a blue jacket, sporting corn rows, and having rather light, tanned skin. The same goes for his sister, Leta.