He appears to be kind of a smart beak, as he likes to tease the members of the family. Bobby does not get along with him (except for one occasion, where he falls for Bobby due to the love potion) but Sergio does apologize for being "a handful" to him in "This Bird Has Flown". Sergio is very intelligent, being able to fly around the neighborhood unattended and speak in complete sentences. He also spends a lot of time dancing to music, both during the day and at night.
He is a parrot, and specifically, he is most likely a scarlet macaw. He has a body mostly made up of red feathers, light orange head feathers, as well as having some light orange in the middle of his wings, blue feathers on the tips of his wings, yellow feet, a yellow upper beak, a black lower beak, grey eyelids, black eyebrows, and oval shapes over both his eyes, that have a tan color on the inner part, a darker tan in the middle, and a reddish pink color at the end.
Sergio's voice actor, Carlos Alazraqui, also voiced the parrot character Paco on the PBS Kids series Maya & Miguel. Interestingly enough, both characters have similar voices, so Paco could be said to be an inspiration for Sergio.
According to Instagram, his real name is "Cupcake," but Abuela doesn't want him to know that.
"Bad Cluck" reveals that he once attended "flight school", where he used to be friends with a chicken named Alfredo, but after Sergio pooped on Alfredo's car, spoiled his birthday party, and stole his sunglasses while Alfredo was in the hospital, they became rivals. The episode also implies that Sergio has wronged a cow before.
"Guilt Trip" reveals that, like Lori, he used to wear glasses and braces and is embarrassed about it.