|Alter Ego(s)||Señor Siniestro|
|First Appearence||El Tigre, El Jefe|
|Voiced by||Jeff Bennett|
Sergio is a very small 13-year-old Italian boy who was transferred to Miracle City.
Sergio is a small Italian teen with a clean cut appearance. He seems to be tagged as a "nerd" to his peers.
When talking to peers at the middle school, he acts nice and understanding. However, secretly he is more diabolical in thought. Although sometimes this personality comes out without him noticing the people around him. Such as him laughing manically when other students are around him, when he notices he stops and said he remembered a funny joke. He has a major crush/obsession on Frida Suárez shown in Wrong and Dance where he was excited with her asking him out even willing to change himself for her. When Frida canceled their date, he was so angry with her that he disregarded that his new bad attitude attracted the attention of three girls who all rejected his rival Manny. He wasn't satisfied with their affections simply because they were not Frida who he swore to make his.
However, as Señor Sinestro, he is much more harder on his foes.
Ever since he was a young child, he dreamed of being a cowboy, so he came to Miracle City in order to fulfil that dream. On his first day of school, he foolishly wore his beloved cowboy costume, complete with a broomstick horsey he called Mr. Broomyhorse. Unfortunately, everyone laughed at him as he was just making a complete fool of himself. Manny helped join in on the laughter (even though he didn't really want to), prompting Sergio to develop a hatred for him.
Relations with Other Characters
Diego/Dr. Chipotle Jr.
He is friends with Diego, secretly Dr. Chipotle Jr. The two ocassionally play video games together in Sergio's barn. They are both aware of each other's secret supervillain personas.
Much like his friend Diego, Sergio has a crush on Frida Suarez. His attempts to woo her are as ineffective as his friend's.
Confirmed by the creator, Sergio at some point in time will date Frida. It is not known how Frida eventually decided to turn her relationship with Sergio further, be it for a love interest or to catch Manny's attention. It is most likely they dated in high school, due to the fact that Manny was involved with Zoe at the time. No information is known on how they break up but Sergio recovers from the rejection by creating a robotic Frida droid or (Frida-bot) to accompany him. Much like his villain counterpart Dr. Chipotle Jr. who created a Frida made entirely out of guacamole (or Guaca-Frida).