Vallejo was with the Safety Patrol for several years before becoming the Junior Commissioner. He has had two partners: Malika and Frank Bishop. Vallejo lost Malika when she infiltrated the Red Robins on an undercover job. She was tempted by the Robins and eventually became their leader.
Frank was not just Vallejo's partner, he was one of his closest friends. However he resigned from the force after throwing a vat of gazpacho at suspect Chatchi Frezno, who turned out to be highly allergic to it. In order to stop Chatchi's parents from suing Principal Folsom, Frank resigned from the safety patrol. Shortly afterward Vallejo was promoted to Junior Commissioner.
Vallejo is pretty stressed. Partially due to Fillmore's behavior as he tends to cause a lot of damage in the field, which Vallejo gets to hear from Principal Folsom. Vallejo also seems to get stressed from Folsom's constant threats on what she will do with the Safety Patrol should they fail to resolve a case.
Vallejo also has a cocoa-addiction. He once unsuccessfully tried to drop the habit.
Even though Vallejo may seem tough on the outside, he does care for his officers. He was afraid that Ingrid would join the Red Robins, like Malika did years ago. He also shows concern for Fillmore when he tends to get too rash as he does not want his best officer to get in trouble.
- Main article: Principal Folsom
Vallejo has mixed experiences with the Principal. On one hand, she constantly threatens to turn the Safety Patrol's office into something else, like a sauna. Whenever a safety patroller makes a grave mistake, Vallejo is the one who gets scolded. On the other hand, Principal Folsom is also eager to compliment the Safety Patrol when they have solved a case. Usually spinning it for public relations as her good foresight for supporting the program.
She did give Vallejo a second term as Junior Commissioner, so she must be satisfied about his work.
- Main article: Cornelius Fillmore
Fillmore is often the prime cause for Vallejo's stress over the of damage which mounts up when he is at work. Vallejo is the one who gets to deal with these damage reports. Fillmore also has an attitude, which causes Vallejo to scream out loud: "FILLMORE!"
At the same time, Vallejo will admit Fillmore is his best officer and tries his best to keep him from going too far.
- Main article: Ingrid Third
Vallejo was unsure of Ingrid's qualities at first. He did not want her to infiltrate the Red Robins, because he had previously seen someone like Ingrid join them. He has since learned to trust her as she did a great job on infiltrating them.
Still, Ingrid can cause some stress because at times she shows the same attitude Vallejo gets from Fillmore.
- Main article: Danny O'Farrell
Vallejo does not take O'Farrell serious, stating him as unqualified to even operate a stapler. He also chose not to get a safety patroller as a replacement when Danny went on a field trip, saying they would only need a tripod.
- Main article: Malika
Malika was once Vallejo's partner. According to him she was a lot like Ingrid. Smart and different from the average student. The main difference was Malika was in a lot of clubs, such as the Unicycle Club; the AV Club; and the Safety Patrol. When the Red Robins became her top priority, Malika quit all of the other clubs she was in. Vallejo took her resignation and defection to the Red Robins pretty hard, and was afraid the same would happen to Ingrid. It is unknown how Vallejo reacted to Malika's arrest.
- Main article: Frank Bishop
Frank was one of Vallejo's closest friends. Vallejo said Frank was the safety patrol's best profiler, that he could even tell what a suspect had eaten for breakfast just by looking at his footprints. Vallejo always regretted Frank's resignation and he seems to have always blamed himself for not standing up for his partner. Vallejo did his best to earn Frank's forgiveness when he agreed to help solve the serial shredder case. Eventually both became friends again and Vallejo even managed to get Frank back with the Safety Patrol as their profiler.
- Vallejo's Cocoa-addiction is an allusion to the coffee-addiction many commissioners in detective series have.
- Vallejo's first name might be a reference to CSI: Miami character Horatio Caine.
- Horatio Vallejo is voiced by Horatio Sanz.
- Vallejo's relationship with Fillmore is an allusion to cop shows' chief officer having an antagonistic relationship with the protagonist.