Diego has brown eyes, short, black hair and tan skin. He wears a short sleeved purple checked shirt.
In Book 2 and Book 3, his hair is much longer and he has a mustache, beard, and goatee. Moreover, his shirt is unbuttoned and there are tears at the edges of the sleeves.
Diego loves parties and is a huge fan of pop culture. Throughout the story, he is constantly making references to various movies and TV shows. He is shown to be very kind and worries about others. He is also probably homosexual or bisexual as in Chapter 14 he tells Your Character about having a crush on one of the guys (Sean, Jake, Raj, Craig). His file in Rourke's database says that he hides certain parts of his personality from his more conservative family.
In Book 2, Chapter 2, it's revealed that he's been living among the Watchers during the last six months.
- "Maybe I was always cut out to be a sidekick, but if so, then I'm glad I was your sidekick."
- —Diego to Your Character.
Diego is Your Character's best friend. Diego also tends to confide his feelings and secrets in Your Character, such as his crush on one of the other male members of the group in Chapter 14. He seems impressed when you think like a detective, such as guessing that Estela being on the plane is suspicious (although it is later revealed that Aleister is in fact the one who isn't supposed to be there) and guessing that the computer password is Zodiac.
In Book 1 Chapter 16, he sacrifices himself to the Vaanti, leaving you riddled with guilt to the point where you hallucinate.
When they are finally reunited in Book 2 Chapter 3, he says he always knew you would come back for him.
He is surprisingly interested in your love life and often encourages you to make a move on your love interest (either Jake, Estela, Sean, or Quinn). This may be because, as shown in the Andromeda Idol flashback, Diego has difficulty being assertive in his own life and is used to living through his friends.
It seems that he has a very strained relationship with his parents.
In Book 2 Finale, a premium choice revealed that he hasn't talked to them for a long time and wanted them to accept him, most likely for his homosexuality. He also said he forgives them.
His Ember of Hope shows a future where his father calls him to apologize for mistreating him in the past.
After capturing Diego, Ximaedra ordered Diego to act as Varyyn's tutor. The two developed a friendly relationship, with Diego covering for Varyyn and Varyyn interceding with the Vaanti on Diego's behalf. He and the other Vaanti call Diego, "Canis", which is his Hadean Zodiac sign. Upon seeing Diego and Varyyn in a seemingly intimate moment (Varyyn braided Diego's hair so he could see better), Your Character asks if Diego and Varyyn are "a thing", which flusters Diego.
After defeating Cetus, Your Character can encourage Diego and Varyyn to have a private moment, which will lead to Diego being somewhat more obvious about his attraction to Varyyn. They will finally share a kiss at the New Year's Eve party. Your Character can later encourage them to share a night under the stars before the infiltration of MASADA. When it is time for the group to step through the Lernaean Gate, Diego and Varyyn share a tearful goodbye, with Varyyn promising to wait for Diego "for eternity".
When trying to get back to La Huerta, Your Character will transmit Diego's Star Wars reference to Varyyn, prompting the young Elyyshar to reopen the Gate, reuniting the lovers. They get handfasted in Book 3, Chapter 10.
- His Hadean Zodiac sign is Canis, the Dog.
- Diego is the only character that already has a very positive opinion of you, as you are best friends with him. Everyone else starts off having a positive opinion about you or less.
- If you did not invite anyone to your room in Book 1, Chapter 14, Diego will be in your room. He will be accidentally murdered by Varyyn before being brought back to life by you using Varyyn's necklace.
- Of the three group members who can be left behind in the finale of Book 1, only Diego's disappearance is non-negotiable, as Raj and/or Grace can be saved as premium choices, whereas Diego's is scripted with no choices.
- Jake calls him "Pop Culture Petey" because of his obsession with movies and his constant references to them.
- He prefers Christian Bale as Batman over Ben Affleck.
- His Ember of Hope shows a future where he writes a bestselling book and becomes a Professor at Hartfeld.
- For the Varyyn and Diego scenes, the writing was inspired by the song, Stay by Rihanna ft. Mikky Ekko. 
- Originally, the character's name was supposed to be Ben.