Gustavo's birthplace and background are both unknown, though in "Big Time Terror" Kelly informs the boys that he did not have fun or play games as a child, because he had to practice playing the piano. (thus in one episode where he was staying with one of the boy's in there family apartment, was was seen messing around and laughing), He can't stand James for some reason, often stating that he reminds him of Matthew McConaughey. He often refers to the boys as "dogs". In Big Time Crib, he treated the boys like an actual dog when they are going to suggest the location for the interview by saying "Heel...Stay...Speak", which made Kelly give him a face. He also has anger management issues, and in "Big Time Terror" he is shown yelling in his sleep. Sometimes, he gets so angry, he once caused an earthquake all the way to Miami Fl. Although he is seen to mostly be angry, he is kind-hearted to animals and seems to get along with them more than people.
Gustavo's blood pressure is always going up when he's annoyed, especially with Kendall because he always talks back to him(Big Time Guru). He has a hard time admiting that the boys are his good luck charms, that he is proud of them and that he likes them. It is noted that he likes the fact that the so-called "dogs" raise his blood pressure and not listen to him (Big Time Mansion).
Gustavo may seem angry or have a frown on his face but inside he deeply cares for the boys. Gustavo may call the boys "dogs" because they are loyal or because he said he can turn a dog into a pop star. Also because he wanted the boys back and said they taught him loyalty, friendship, and family. Also, he does treat the boys like dogs when helping them to record songs.Gustavo usually has a hard time with the boys, but he seems to get along more with Logan than any of the others. Probably because Logan has the type of 'not-gonna-do-the-bad -thing' attitude but it is true that he always follows his friends however, he isn't the one that come up with the crazy schemes and occasionally tries to stop the others from doing them. It is also shown the only family members he knows of Big Time Rush is Kendall's mom and sister,Carlos's dad, and some others. He and Kelly are very close and have a good friendship. She usually goes along with Gustavo's schemes and plans even though she doesn't really want to do them. (See Gustelly)
In Big Time Concert, Kendall said that Gustavo is loud, mean, obnoxious, self-absorbed, and very unattractive. His behavior is the reason Kendall made up The Giant Turd Song. Gustavo once called the boys "monkeys" to which Logan replied "I thought we were dogs", and Gustavo corrected "You're monkey-dogs!". In Big Time Concert, he said that he's not good at good byes.
As the story progressed Gustavo shows some affection to the boys. In Big Time Camping, he is worried about the boys getting hurt or sick. And he admitted that he feels like being a parent to them. In Big Time Rescue, it is revealed that he loves the boys (the hint of the secret vault's password is "Something You Love") and he use "My Dogs" as his secret vault password.